Like Rhia, I think that replicators would be awesome... but not just for food... those damned things can reproduce nearly anything!
Aside from that, I'd have to say that I have two favorites that I think would be awesome: holograms/holodecks (interactive video games!
) and teleporters. The former would just be cool as hell and would excite the little gamer girl inside of me to no end, and the latter would make living long distance from my Love
far more tollerable!