My first try at a Sunny Day team or Uber team, so don't be too critical.
Groudon @ Lum Berry
Drought
252 Attack/252 Speed/4 HP
Jolly
~Earthquake
~Fire Punch
~Thunder Wave
~Stealth Rock
Ah, Groudon, a great lead in Ubers. Earthquake hits most things very well. Fire Punch is for those annoying Scizors. Now for the other 2 moves. What I can't Thunder Wave, I Stealth Rock. What I can't survive a hit from, I Thunder Wave. Lum Berry stops Darkrai's main purpose.
Tangrowth @ Leftovers
Chlorophyll
252 Attack/252 Speed/4 HP
Impish
~Power Whip
~Knock Off
~Sleep Powder
~Stun Spore
An NU Pokemon on an Uber team? You're crazy. Well, I don't care. Tangrowth is awesome, look at it. As you can see, this is the Double Powder set with some modifications. Power Whip does crazy damage with STAB. Knock Off ruins the point of Trick in Ubers. The rest of the set is self-explanatory.
Ho-oh @ Expert Belt
Pressure
252 Sp. Attack/252 Speed/4 HP
Jolly
~Sacred Fire
~Earthquake
~Solar Beam
~Recover
Stealth Rock has completely ruined Ho-oh's credibility as an Uber. Sacred Fire is the sole reason this pokemon is Uber in my opinion. Earthquake is for Electric and Rock types trying to destroy my Ho-oh. Solar Beam is perfect for a Sunny Day team for obvious reasons as it destroys any counter to Ho-oh. Recover to ware off Stealth Rock damage.
Jirachi @ Leftovers
Serene Grace
252 Sp. Attack/252 Speed/4 HP
Modest
~Psychic
~Shadow Ball
~Wish
~Thunderbolt
This set is pretty self-explanatory.
Heatran @ Focus Sash
Flash Fire
252 Sp. Attack/252 Speed/4 HP
Timid
~Flamethrower
~Flash Cannon
~Earth Power
~Stone Edge
If a counter to Jirachi comes in and knows a Fire type move, Heatran can counter it and get some speed. The rest is also pretty self-explanatory.
Giratina-Regular @ Leftovers
Pressure
252 Sp. Def/252 HP/4 Sp. Attack
Gentle
~Dragon Pulse
~Shadow Ball
~Aura Sphere
~Will-o-Wisp
Groudon @ Lum Berry
Drought
252 Attack/252 Speed/4 HP
Jolly
~Earthquake
~Fire Punch
~Thunder Wave
~Stealth Rock
Ah, Groudon, a great lead in Ubers. Earthquake hits most things very well. Fire Punch is for those annoying Scizors. Now for the other 2 moves. What I can't Thunder Wave, I Stealth Rock. What I can't survive a hit from, I Thunder Wave. Lum Berry stops Darkrai's main purpose.
Tangrowth @ Leftovers
Chlorophyll
252 Attack/252 Speed/4 HP
Impish
~Power Whip
~Knock Off
~Sleep Powder
~Stun Spore
An NU Pokemon on an Uber team? You're crazy. Well, I don't care. Tangrowth is awesome, look at it. As you can see, this is the Double Powder set with some modifications. Power Whip does crazy damage with STAB. Knock Off ruins the point of Trick in Ubers. The rest of the set is self-explanatory.
Ho-oh @ Expert Belt
Pressure
252 Sp. Attack/252 Speed/4 HP
Jolly
~Sacred Fire
~Earthquake
~Solar Beam
~Recover
Stealth Rock has completely ruined Ho-oh's credibility as an Uber. Sacred Fire is the sole reason this pokemon is Uber in my opinion. Earthquake is for Electric and Rock types trying to destroy my Ho-oh. Solar Beam is perfect for a Sunny Day team for obvious reasons as it destroys any counter to Ho-oh. Recover to ware off Stealth Rock damage.
Jirachi @ Leftovers
Serene Grace
252 Sp. Attack/252 Speed/4 HP
Modest
~Psychic
~Shadow Ball
~Wish
~Thunderbolt
This set is pretty self-explanatory.
Heatran @ Focus Sash
Flash Fire
252 Sp. Attack/252 Speed/4 HP
Timid
~Flamethrower
~Flash Cannon
~Earth Power
~Stone Edge
If a counter to Jirachi comes in and knows a Fire type move, Heatran can counter it and get some speed. The rest is also pretty self-explanatory.
Giratina-Regular @ Leftovers
Pressure
252 Sp. Def/252 HP/4 Sp. Attack
Gentle
~Dragon Pulse
~Shadow Ball
~Aura Sphere
~Will-o-Wisp