Eclipse is — or was, I haven't used it since 2006 — also great. Instead of using the horribleness that is Swing, they wrote their own toolkit, SWT, which uses n

Eclipse is — or was, I haven't used it since 2006 — also great. Instead of using the horribleness that is Swing, they wrote their own toolkit, SWT, which uses native UI controls, and it's the only Java app I've ever used that had a native look and feel. (They did a lot of custom rendering, of course, but it was still able to feel native.)