I would have to say going with the Intel® Core™ i3-2100 and a Asus P8Z68-M Pro board (Micro-ATX, but that shouldnt matter as it will give you the PCI-e 16X slot that you are looking for and at $130 it is a really nice board.
This is coming from a longtime AMD fan, I am seriously considering Intel next build. I talked to a Microcenter Rep who had an AMD Phenom II x4 970, and he just got the i7 2600K and said basically there is no comparison. I've been using AMD processors since the days of the AMD K-6 processors, and I'm starting to think an i5 2400 or 2500K is sounding good to use.
with your budget, intel is a bit expensive, if ur not going to over clock, jus stick with amd, an x4 processor, motherboard, try something along the lines of ASUS M4A88T-m-USB3 its a ddr3 board, will work crossfire but not sli, as per individual cards, yes it will work nvida/amd.