The Trio!

[Supaskillz]

Shaman+monk+anything makes a pretty good trio. A variety of trips would work though. Cleric, tank and ench is another great one. Even the ranger necro shaman is doable. Especially if you pick outdoor dungeons where ranger can harmony(Casio Thule, karnor, city of mist), but it can work elsewhere as well since all 3 of you can root for crowd control, necro gets a short term mez and ranger and necro can help out shaman a bit with the heals. Most trios can find a way to make it work, even indoors, but some may not be as efficient as others