Three words: Schwalbe Marathon Pro

I have them on my old MTB, they feel a heck of a lot faster than the knobbies it came with, and they cope reasonably well with gravel and that sort of thing. Only one puncture in 8 months (can't tell you how many miles, quite a few) and that was from a thorn about half an inch long, and the tyre went down very slowly until I dug the thorn out. If my commuter wasn't 700C, I'd have them on that as well.