I use Netbeans, http://www.netbeans.org/. It's nice and free. I'm not sure if that's the most popular editor nowadays, but it's the one I still use.
I use Eclipse but thats really a matter of taste. Try out textpad, jcreator, intellidea (or something like that, forgot the name of the IDE) netbeans etc and stick with the one you are most comfortable with.
Yep, I used to use Eclipse, too. Then my boss decided to have us switch to Netbeans, for what reason I have no idea, really.