If I were you I would just stick with what you got for a little while longer. You see alot of people with AMD CPU's these days because they are cheap and it makes it more affordable to build a system. The Q9450 you have at 3.3ghz is plenty of power for gaming and just about anything else. Your money would be better invested in a better GPU if you are a gamer or maybe a good SSD drive might be a good upgrade too. This all depends on your main uses for the computer, but there is no reason that I can see to upgrade since anything that you can get between $200 - $250 will offer no better performance then what you got.
Just as a little note the high end core 2 CPUs are still faster clock for clock then AMD's offerings so there is no point to look at new CPU's especially since the AMD Phenom II x4's would actually be a downgrade from your current CPU.