Swype has been my favorite way to type on an Android phone, but it's been kinda limited in what phones can run the keyboard software. Until now! All you have to do is register at Swype and download.
There are plenty of keyboard "improvement" apps on the Marketplace meant to improve Android's typing experience. Two reasons: because the Android soft-keyboard sucks, and because Android is open enough that they can. ThickButtons is a pretty good evolution of this.