<p>The last cross platform desktop development I did was Java/Swing.  What about flex?</p>

I've used
RealBasic from RealSoftware
for a few things just to play with it.  It can get expensive if you need the pro version.  It will allow you to build a stand alone binary for Linux, MacOS X, or Windows.  I'm more of a server side guy but it was pretty straight forward to create the few tools I wanted to try making with it.