MF + Sona = Level 6 double kills. Great poke and sustain.
Cait + Taric = Great Zoning, poke, and sustain.
Sivir + Soraka = Vs any Caitlyn, Nunu, Taric combo. Great poke, burst, and sustain.
Alistar + Vayne = Pin people to walls until they are dead. Has good sustain and kill potential but can be out-poked.
Leona + Trist, Ezreal, Graves, or Corki = Kills..
Lux + Ezreal = Great poke comp with kill potential. Can out-zone Caitlyn, foreelz.
Nidalee + Caitlyn = Great poke comp with lane control and sustain.
Personally my 3 favorites are Cait+Taric, Sivir+Soraka, and Vayne+Alistar.