CPU? How much money do you have left for a CPU after everything else?
If you can afford $215, get a $180 Q6600 OEM and a $35 HDT-S1283 cooler. That should solve your problem for a few years.
If you've got only $170, get an E8400 retail (and add a better cooler later, if you want to overclock).
If you're closer to $120, E7200.
In games, a quad (Q6600) and a slightly higher-clocked dual (E8400) will be very close. There are exceptions, like FSX where the quad kicks a$$, but in general the dual wins. Of course, if you run things in the background while playing, the quad may win again. And most times the HDD or GPU will be the limiting factor and you'd get exactly the same fps with either CPU.
If it's a long term thing get the quad, it will be better once more games start using 4 cores.