LÖVE

If you're the kind of (mainly 2d) graphics programmer that I am, the thing you find most attractive about Processing is the one-click publishing to make a webpage and show people what you've been doing. Everything else after that is a bonus.

If you're not that kind of programmer, and the web isn't your primary concern, then you should definitely check out LÖVE. It looks like they're having a lot of fun over there, and Lua is just nicely mind-bending enough but still familiar if you're coming from Java or Actionscript.