Status: Ready! (More suggestions and proofreads are always welcome)http://www.smogon.com/dp/pokemon/metagross
Team options italicized (the last paragraph).
Updates:
I've been using this set for a few days now, trying to tweak the EVs every now and then. So far I like it (I've been primarily pairing it with a Gyarados). It's REALLY bulky once it sets up screens, most non super-effective special attacks doing only a pathetic 15%-30% and experiencing similar results from the physical spectrum. The boom I can use (Explosion) after setting up the screens is helpful as well.
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[SET]
name: Dual Screener
move 1: Reflect
move 2: Light Screen
move 3: Explosion
move 4: Earthquake / Meteor Mash
item: Light Clay
nature: Careful
evs: 252 HP / 72 Def / 176 SpD / 8 Spe
[SET COMMENTS]
<p>Pokemon with outstanding offensive power often find their attacking stats overshadowing their supportive prowess. This is especially true for Metagross. While most dual screen users are specially-based, Metagross brings different tools to the table. Firstly, contrary to what its Psychic-typing suggests, Metagross is actually a physically-based Pokemon. Its high Attack can exploit a threatening Earthquake, STAB-boosted Meteor Mash, or a formidable Explosion that makes way for an incoming teammate. This describes the difference between Metagross and Bronzong - Metagross is not only a defensive screener, but also an offensive screener as well. Secondly, even before the support of both Reflect and Light Screen, its bulk borders high levels. This allows it to accomplish its job with consistent ease.</p>
<p>This Metagross' EVs are specifically configured to set up on its long-time rivals. The given spread of 252 HP / 72 Def / 176 SpD / 8 Spe and a Careful nature attempt to allow Metagross to set up on opponents that give it the most problems, including Magnezone, Heatran, and Dugtrio. This Metagross will outrun 172 HP / 252 SpA / 84 Spe versions of Magnezone and OHKO them with Earthquake. If the Magnezone is faster, worry not; one Thunderbolt before (and two after Light Screen) will never 3HKO you, factoring Stealth Rock damage. You can then use Reflect and then Explode, which can hugely dent but unfortunately not OHKO Magnezone. Heatran is a tougher story altogether, and the very best you'll be able to do against it if it uses Fire Blast is set up dual screens (logically, you can also use Earthquake to OHKO it if you have set up Light Screen). If it uses Earth Power, one without Light Screen will do 45%-53%, and an Earth Power after a Light Screen will do 22%-27%. You will usually be unable to survive Heatran's third assault, so most of the time you will have to settle for the fact that Metagross will only be able to set up dual screens. The next troublesome opponent is Dugtrio. If you wish to be able to both set up dual screens and defeat it, you will need to set up Reflect as it switches in. Jolly Choice Banded Dugtrio's Earthquakes will then do only 43% damage at max, allowing you to set up Light Screen, survive even if you have taken prior Stealth Rock damage, and Explode.</p>
<p>Metagross' moveset requires a brief elaboration. The first three moves are the vital constituents of this set and are thus irreplaceable. Metagross' fourth moveslot, however, can be debated on. While Metagross' STAB-boosted Meteor Mash may seem like the more favorable option, Earthquake has proven to be the superior choice. It allows Metagross to score crucial OHKOs on Magnezone and Heatran, suddenly making Meteor Mash a mediocre choice. Although Meteor Mash can harm defensive versions of Gliscor and Hippowdon, both of them can heal themselves anyway. Moreover, Explosion will either OHKO or gravely wound them to the point that an incoming sweeper can finish them off. Other options that can be used include Stealth Rock or other attacking moves like the elemental punches. Substitute can even be used to scout incoming foes. In spite of all these choices, Earthquake still seems to be the most appropriate move.</p>
<p>Support for this Metagross can prove useful but is not mandatory, as its objective is simply to set up dual screens, OHKO something if possible, and/or use Explosion. Therefore, you should focus on teammates that can abuse the active dual screens instead. Gyarados and Metagross can cushion each other's weaknesses; Gyarados can also use numerous Dragon Dances to set up under dual screens. Latias also functions similarly to Gyarados, with the added bonus of Metagross resisting more of its weaknesses, but employs Calm Mind instead of Dragon Dance. A teammate that can eliminate Rotom formes and set up along the way will also prove useful. Examples of these include Dragon Dance Tyranitar and Curse Snorlax. Teammates do not always have to appear in the form of set-up sweepers, though. Gliscor partners well with Metagross, can abuse Rock Polish and Swords Dance, and Baton Pass their effects to other teammates. Celebi can Baton Pass Calm Mind or Swords Dance, while helping Metagross with its Swampert problem. Any other teammate that can offensively make use of the multiple turns and defensive barriers that the dual screens provide are generally key partners to this set. Examples include, but are not limited to, Dragon Dance Salamence, Torment Heatran, and Calm Mind Suicune.</p>
Team options italicized (the last paragraph).
Updates:

I've been using this set for a few days now, trying to tweak the EVs every now and then. So far I like it (I've been primarily pairing it with a Gyarados). It's REALLY bulky once it sets up screens, most non super-effective special attacks doing only a pathetic 15%-30% and experiencing similar results from the physical spectrum. The boom I can use (Explosion) after setting up the screens is helpful as well.
------------------------------------------------------
[SET]
name: Dual Screener
move 1: Reflect
move 2: Light Screen
move 3: Explosion
move 4: Earthquake / Meteor Mash
item: Light Clay
nature: Careful
evs: 252 HP / 72 Def / 176 SpD / 8 Spe
[SET COMMENTS]
<p>Pokemon with outstanding offensive power often find their attacking stats overshadowing their supportive prowess. This is especially true for Metagross. While most dual screen users are specially-based, Metagross brings different tools to the table. Firstly, contrary to what its Psychic-typing suggests, Metagross is actually a physically-based Pokemon. Its high Attack can exploit a threatening Earthquake, STAB-boosted Meteor Mash, or a formidable Explosion that makes way for an incoming teammate. This describes the difference between Metagross and Bronzong - Metagross is not only a defensive screener, but also an offensive screener as well. Secondly, even before the support of both Reflect and Light Screen, its bulk borders high levels. This allows it to accomplish its job with consistent ease.</p>
<p>This Metagross' EVs are specifically configured to set up on its long-time rivals. The given spread of 252 HP / 72 Def / 176 SpD / 8 Spe and a Careful nature attempt to allow Metagross to set up on opponents that give it the most problems, including Magnezone, Heatran, and Dugtrio. This Metagross will outrun 172 HP / 252 SpA / 84 Spe versions of Magnezone and OHKO them with Earthquake. If the Magnezone is faster, worry not; one Thunderbolt before (and two after Light Screen) will never 3HKO you, factoring Stealth Rock damage. You can then use Reflect and then Explode, which can hugely dent but unfortunately not OHKO Magnezone. Heatran is a tougher story altogether, and the very best you'll be able to do against it if it uses Fire Blast is set up dual screens (logically, you can also use Earthquake to OHKO it if you have set up Light Screen). If it uses Earth Power, one without Light Screen will do 45%-53%, and an Earth Power after a Light Screen will do 22%-27%. You will usually be unable to survive Heatran's third assault, so most of the time you will have to settle for the fact that Metagross will only be able to set up dual screens. The next troublesome opponent is Dugtrio. If you wish to be able to both set up dual screens and defeat it, you will need to set up Reflect as it switches in. Jolly Choice Banded Dugtrio's Earthquakes will then do only 43% damage at max, allowing you to set up Light Screen, survive even if you have taken prior Stealth Rock damage, and Explode.</p>
<p>Metagross' moveset requires a brief elaboration. The first three moves are the vital constituents of this set and are thus irreplaceable. Metagross' fourth moveslot, however, can be debated on. While Metagross' STAB-boosted Meteor Mash may seem like the more favorable option, Earthquake has proven to be the superior choice. It allows Metagross to score crucial OHKOs on Magnezone and Heatran, suddenly making Meteor Mash a mediocre choice. Although Meteor Mash can harm defensive versions of Gliscor and Hippowdon, both of them can heal themselves anyway. Moreover, Explosion will either OHKO or gravely wound them to the point that an incoming sweeper can finish them off. Other options that can be used include Stealth Rock or other attacking moves like the elemental punches. Substitute can even be used to scout incoming foes. In spite of all these choices, Earthquake still seems to be the most appropriate move.</p>
<p>Support for this Metagross can prove useful but is not mandatory, as its objective is simply to set up dual screens, OHKO something if possible, and/or use Explosion. Therefore, you should focus on teammates that can abuse the active dual screens instead. Gyarados and Metagross can cushion each other's weaknesses; Gyarados can also use numerous Dragon Dances to set up under dual screens. Latias also functions similarly to Gyarados, with the added bonus of Metagross resisting more of its weaknesses, but employs Calm Mind instead of Dragon Dance. A teammate that can eliminate Rotom formes and set up along the way will also prove useful. Examples of these include Dragon Dance Tyranitar and Curse Snorlax. Teammates do not always have to appear in the form of set-up sweepers, though. Gliscor partners well with Metagross, can abuse Rock Polish and Swords Dance, and Baton Pass their effects to other teammates. Celebi can Baton Pass Calm Mind or Swords Dance, while helping Metagross with its Swampert problem. Any other teammate that can offensively make use of the multiple turns and defensive barriers that the dual screens provide are generally key partners to this set. Examples include, but are not limited to, Dragon Dance Salamence, Torment Heatran, and Calm Mind Suicune.</p>