The defaults in Netbeans are pretty decent, but here are a few changes I like to make. You should create a new profile in Preferences -> Fonts & Colors, to be able to go back to the defaults easily.
The first change I've made is change the default font to Monospace 13. To make fonts look better, switch to the Apple's Quartz rendering engine. To do this add the following
-J-Dapple.awt.graphics.UseQuartz=true
to the
netbeans_default_options in the netbeans.conf file. Which can be found at
/Applications/NetBeans/NetBeans 6.5.app/Contents/Resources/NetBeans/etc/netbeans.conf
Textmate also uses bold face for keywords, this is something I really like, and is another change I've made. I've also set the application font to 11, this can be done with
--fontsize 11
