For me the 21/22 " Cintiqs are where you want to be. The small ones are no use as actual monitors and the giant ones are just a pain in the arse to operate. I'm too tight to buy one with my own money so I got a monoprice 22 instead and I'm very happy with it.
personally I'm still on my black 21" UX. I'll use this thing until it stops working. Only downside is that it's 4:3 which makes playing some games weird but, eh. It's fine. You can usually find it for under 700 these days, methinks. Lots of great suggestions in this thread though. I think if this did die I'd see how the 16…