I'm working on an open-source Java Web Start application, and I'd like to give it a consistent theme across platforms. Metal is totally ugly, and I'm not particularly happy with Substance (esp. performance). What are the best Swing Look&Feel options out there today?
Check out JGoodies, its the de facto standard place to start for a decent L&F.
I have found the using the "native" L&F consistently results in applications that look "right" for the specific platform. But JGoodies is an excellent across-the-board alternative.
For myself, I don't care if an app looks "native", as long as it looks just as professional and at least as good. FWIW, I don't think the that Java "Metal" or "Ocean" looks achieve either one.
That said, be careful... for many users the only thing which will look "good" is that which is the same as every other application on their platform. The only UI that I think consistently trumps all for looks is the current Apple OSX look - but even that looks out of place when it's the only such app in my Windows desktop.
The Alloy Look and Feel is pretty good IMO, but it costs $$$ http://lookandfeel.incors.com/
I like the 'Nimbus Look&Feel'(2nd image) introduced in Java 6 Update 10 very much and it is contained in SUN's vanilla J2SE of J6u10 and later by default!
Another advantage is, that it is painted entirely using Java 2d which makes it fast and rederable at all resolutions.