Venusaur
Ability: Chlorophyll
A base speed of 80 is a bit meh, but in sun it will double, and Venusaur's good typing will mean that it'll be immune to Toxic while also removing Toxic spikes. Growth will now double its Attack and Special Attack in sun, meaning it can either use a physical/ special/ mixed moveset.
Lilligant
Ability: Own Tempo/ Chlorophyll
While Own Tempo may seem useless, Lilligant has access to the high attack move of Petal Dance, which (like Outrage) causes confusion when it ends. With Own Tempo, it will not become confused at the end of this move.
Chlorophyll is the main ability used in OU, since it will double her speed, but with access to Sleep Powder and Quiver Dance, Lilligant can consider Own Tempo as its more favourable ability if it's not using Solarbeam. Indeed, Solarbeam is useless if you end up facing a Rain team, and Politoed switches in just as pick Solarbeam (since a lot of Politoeds will have Protect).
Shiftry
Ability: Chlorophyll
An absolutely horrible typing, Shiftry abuses its mediocre speed doubled in sun, its passable attack and acceptable special attack. Shiftry is usually seen holding a Life Orb, and will be able to be either a physical or special sweeper, having access to Swords Dance and Nasty Plot.
Jumpluff
Ability: Chlorophyll
Usually a NU Pokemon, Jumpluff sees use with a base speed of 110 doubling in the sun. Access to Encore, Leech Seed, Sleep Powder and U-Turn means it can function in the same way Whimsicott can with Prankster, but it will be able to escape much faster.
Infernape
While Infernape doesn't have an ability that benefits specifically under Sun, it is a popular member on sun teams because of its high attack and special attack, and fire moves will be boosted by weather. In addition, it's typing means it's only affected x1 by Stealth Rock, not x2; Stealth Rock can cripple most Sun Teams since they carry a lot of fire Pokemon.
Tentacruel, Starmie & Donphan
While it might seem strange to carry Water Pokemon on a Sun team, these three Pokemon all serve the same purpose as rapid spinners. The first two will be able to function under Rain, while Donphan will be able to take electric hits. Along with Donphan's Sturdy, it can get rid of Tyranitar with one STAB Earthquake.
Jellicent
Ability: Water Absorb
Jellicent is your rain counter and rapid spin blocker. It access to Will-O-Wisp and Recover means it can stall many physical attackers, and even take x2 hits without fainting.
Shaymin-Sky (Ubers)
Ability: Serene Grace
Yay! 60% flinch chance with Air Slash! Your opponent will hate you forever. Seed Flare makes a good variation from Solarbeam, because if your Sun should end, it at least won't take 1 move to charge and be halved in power in rain. If you should so decide, Shaymin has the move Synthesis, which will replenish its health by 2/3 in sun.
Reshiram (Ubers)
Ability: Turboblaze
Reshiram's ability will negate Flash Fire on Pokemon like Heatran, therefore meaning it can set up Flame Charge speed boost. STAB Fire in power uped by Sun, along with STAB Dragon moves much needed to clear away many Dragon types that dominate Ubers.
Zekrom (Ubers)
While Zekrom does not benefit Sun, it's usage on a Sun team is mainly to counter Kyogre. One STAB Fusion Bolt, along with max attack EVs and favourable nature will OHKO your weather rival, meaning Groundon can set up Drought.
Excadrill (Ubers)
Ability: Mold Breaker/ Sand Rush
Excadrill's sparse movepool is all it needs to function in Ubers. Earthquake is there to deal with Tyranitar, and should you choose Sand Rush for its ability, it will be able to outspeed its weather rival. Along with steel/ ground typing, it's immune to toxic and thunder wave, along with other useful resistances. Excadrill also functions as a Rapid Spinner, and with Mold Breaker will be able to hit Levitate Pokemon with Earthquake.
Basically, anything with Chlorophyll will benefit from Ninetales/ Groundon's Drought. Leaf Guard is an ability which prevents status ailments in sun, but its distribution is limited and the Pokemon who have either have Chlorophyll or a better ability to use. Umbreon and Espeon may be seen as well, since they have Moonlight/ Morning Sun which are boosted by sun.
