My brothers, my dad, and I plan to run a 4 man party with 2 barbs, 1 wizard, and a monk. Both my younger brother and my dad just love playing barbarians (my younger brother is very skilled gamer, and I think the skill gap for playing a barb in Inferno is going to be pretty high so that works out), I don't mind playing a support monk, and 4 melee seems overkill so we're probably going to have a wizard as our fourth slot. It seems like a pretty well rounded group, and given that PVP is 3v3, we can run a barb wizard and monk PVP team which should work well enough.
What about you guys? Do you have any plans for a 4 man group in D3?