@Salac Berry
Nature: Jolly
EVs: 252 HP, 228 Spd, 28 Def
~Spider-Web
~Baton Pass
~Endure
~Poison Jab/Night Shade
Ariados, the one trick pony. With a total HP investment, and enough speed, he can actually pull off a his one trick. The Jolly nature and 228 speed is to beat out base 80 Pokemon after the Salac, which is what you'll want to try and trap.
Switching in is not Ariados' game though, so it'll have to start, or be a revenge 'trapper'. You start with Spider-Web to trap, and take a huge hit probably. You'll want to stick to the physical end of things, unless you resist the special attack. You Endure the following hit, and activate Salac Berry. Then proceed to pass the speed boost+trap, of course.
Without any sort of investment into attack, Ariados' ability to deal damage is limited. If you go with Night Shade, you'll at least assure yourself a bit of damage when the spider comes back out later on. If it could possibly pull off another attack again. Heh.
Now those ridiculous damage calculations. All of these calculations consider 252 EVs into Attack.
Adamant Life Orb Dragonite Fire Punch Damage: 90.41% -
106.40%
Adamant Life Orb Tyranitar Crunch Damage: 72.38% - 84.88%
Adamant Choice Band Tyranitar Crunch Damage: 83.14% - 97.67%
Adamant Choice Band Abomasnow Ice Punch Damage: 60.17% - 70.93%
Adamant Life Orb Electivire Fire Punch: Damage: 85.17% -
100.00%
Adamant Expert Belt Electivire Fire Punch: Damage: 78.49% - 92.15%
Adamant Leftovers Metagross Meteor Mash: Damage: 69.77% - 81.98%
Adamant Life Orb Metagross Meteor Mash: Damage: 90.41% -
106.40%
Adamant Choice Band Metagross Earthquake: Damage: 69.48% - 81.69%
This is, of course, if you want to even think about using it in OU. Fun. :)