This is the fist time i've tried to put a build together for a computer so feel free to point out things that may not work out. I just had a few concerns.
1. Are there any bottlenecks that might be slowing this build down?
2. Is the case I've picked big enough to house everything? I may want to add a second GPU at some point.
3. Will it be easy to overclock? Is the HSF I have good for overclocking?
If your budget is 1200-1500, I would buy i7-9xx series with a compatible motherboard and triple channel 6GB RAM. I would also go with a slightly higher grade card. E.g. HD5870. or GTX470/480. Stick to XFX, HIS for radeons.
Rest all is pretty much a no-brainer. CPU Mobo GPU and RAM matter the most. Your PSU is sufficient for future upgrades. You can very well buy a 650W and be content with it even for SLi or Crossfire but stick to Corsair for its warranty.
I am not sure about the after-market cooler. No knowledge.