Agreed with dangerstat that the i7 and AMD 955 gaming performance is very similar. In most games you will be graphics bound - so the CPU isn't the bottleneck, the GPU is.
That said, I have to disagree with the GTX 260 being the best bang-for-the-buck GPU.
This card must surely take that crown. Also, make note that all the best AM3 motherboards (the 785/790 chipsets) only support crossfire not sli - so an ATI card is preferable with these setups if you plan to add a second card later (as prices come down and crossfire scaling is very good).