Thanks for all the answers.

Never thought of overclocking my CPU because my current cooler is the default one.

And about that extra RAM, does it need to be from the same brand as the others or just the same amount of RAM and Mhz?

I just want some advice before I buy anything for my Rig.

This is my current Rig:

NVIDIA GeForce GTX 560 Ti

AMD Phenom(tm) II X4 965 3.40 Ghz

Gskill Ripjaws DDR3-1600MHz 3x2GB

What should I upgrade first?

About the budget let's say 300? per upgrade.