My favorite CPUs on earth right now are C3 revision Phenom II X4 Black Edition 955's and 965's, both 125w.
They go over 4ghz very easily, made even easier by the unlocked multiplier. And at under 200 dollars they are insanely affordable. They hang very close to equal with the big expensive Intel boys in gaming too.
If you are on a super tight budget, the Athlon II X4 620 Propus @99 dollars is an insanely good deal. Low stock speed but they oc very well.
Also the Phenom II X3's are very very good for gaming, as the fourth core only adds a little bit to gaming, and even then only with multitasking going on. With little to nothing else running in the background, a quad core cpu offers very little over a tri-core in games.
But for general use I far prefer a quad core. I would take the Athlon II X4 620 over a PhII X3, cuz while I game a lot, I also encode and do other stuff that uses all 4 cores.
Good luck, get a good name brand AM2+(for ddr2) or AM3(for ddr3) 785G or 790FX/GX mobo, with an sb750 or sb710 southbridge, and you cannot go wrong.
