I recommend Eclipse.
In response to Russell's post on IDE's, I figured I'd give my opinion. I hate IDE's - for the past couple of years, I could never bring myself to use one for a few reasons (1) too slow, (2) I liked HomeSite too much and it worked for all my Java dev needs, and (3) I didn't like the UI's - not pretty enough for me. Granted, most of these are bad reasons, but we're allowed our opinions right? But with Eclipse 2.0, it's given me enough value-add that I now use it everyday, over IDEA and Sun ONE Studio 4 (a.k.a Forte for Java). It's still slower than HomeSite, but I really like it's look and it does everything I need (although I still use Ant to compile/deploy).