I recently upgraded from my old G1. As I'm on a family plan with AT&T, my selection was rather limited. The Samsung Captivate is the only current generation Android phone available, so I went with it. Fortunately, it turned out to be a great purchase.
The Galaxy S line in general is probably your best choice at this point. With graphics equivalent to a PS2, it hopefully won't go obsolete TOO soon. In addition, the AMOLED screen is the best I've seen. Even on minimum brightness, it remains visible in sunlight.
A friend of mine is getting a Droid X soon, so hopefully I'll have a chance to play around with that.