I got rid of my iPhone 3G last month as I too thought it was painfully slow (and it wasn't jail broken).
Changed to the HTC Desire S and I have to say I'm impressed with it. Extremely quick, especially on the web. Not as much android stuff as there is for the iPhone, but most of the iPhone stuff I downloaded I never used anyway. Battery life isn't great (better than the iPhone, but still needs charging almost every day if you use the Bluetooth and WiFi a lot), but all smart phones are like that to be honest.
E-mail and internet access is brilliant. Video is nice as well. Music isn't in the same league as the iPhone, but I have an iPod anyway.
All in all, it performs very well. Worth a look.