Whatever you do don't get the XtremeAudio. They're just rebranded Audigy SE's for twice the money and aren't real X-Fis. The only X-Fi I would really get is the Gamer (or Music but they're discontinued) because the other ones aren't worth it. To save a few bucks you could try to find either one used, and just fyi the music is exactly the same as the gamer except that you can mod the music for upgrades.
No reason to upgrade you graphics right now since your current should be doing well in the games right now and there will surely be price cuts soon. Rumor is that nvidia is dropping prices on the whole line really soon so at least wait and see if it's true.
If you decide you want 4gigs you know that you do need 64bit windows to use it all. I think 4gigs could start making a difference for games like Crysis so it could be a useful upgrade that you could do right now since I really doubt RAM prices will fall much lower and if anything, I think they'll get higher.
And you say you want a HSF? You're running with stock right now? If you are you could probably easily push that thing to like 3.5+ with a real HSF. You can get tuniqs for like $55 shipped now.