I have been through a raft of android phones and the one I have now settled on is the Samsung Galaxy S (16Gb).
Cracking phone, does everything I need and is nice and light too. Battery life with heavy use is about a day although with light use, and running the Juice Defender app, I can get 2- 3 days out of it.
You can't go wrong with the HTC Desire.
I'm really pleased with mine and my teen son now wants one too!