My new PvE team has

one pally tank
two warlocks
one shadow priest
one restoration shammy

all to-be, they are still little and not really specced yet.

here's why I chose those. Pally tank is relatively easy to play, excellent for aggroeing multiple mobs and gives very good buffs to the party. Warlocks have soulstones (wipe recovery), bloodpact and when specced affliction, they don't burst too much for the pally to tank up against. 2 x Seed of Corruption at level 70 should be awesome. The shadow priest pretty much ensures that the other guys don't run out of mana. Stamina buff, emergency healing, and fear warding are nice too. Now the reasons for a shammy as a healer are: Wrath of air totem (101 spell damage, excellent for the tank and pretty good for the rest), tremor totem, healing/mana stream totems, earth shield and, of course, chain heal and the good old ankh.
I think this setup synergizes pretty well, as they are all casters (pally too). The drawback is the limited crowd control (succubus, fear).
They are only level 8 atm, so I could still change the team if you give me reason to^^.

Cheers.