It comes to just under $1000 after rebates, and it should be fairly simple for you to search the parts on NCIX or newegg.ca. If you find that it goes over your budget, then replace the case with something like the CoolerMaster HAF 912, and you should meet your budget.
Overclocking: Pushing your processor farther than the stock settings. Any Intel processor with a "k" after it overclocks well. This is very safe as long as you're not stupid about it, and is done completely through software/BIOS (you don't actually touch the chip)
SLI/Crossfire: Running two+ GPUs simultaneously... you won't need it atm
So, building on what Merueth put in... get a CPU cooler. Some good ones like a Zalman should be okay. This is only if you're overclocking. If you're not, tell us! I'd suggest a moderate overclock, though.
The case I would switch out for a Corsair 400R
I'd upgrade to a 1TB HDD (still 7200rpm Samsung) because it's only like $20 more
After that, if you have enough, try to upgrade to a 670 for the GPU.
Thanks for the build suggestion. I will probably end up overclockig then. What CPU cooler do you recommend? I was thinking 1TB HDD as well. Would a 670 GPU put me over my budget? I'm unable to check at the moment, sorry.
I would get the CoolerMaster TPC-812. Would still leave you under budget. I can't see a way of getting a 670 in there without going at least a little over and that would involve cutting corners somewhere in either the PSU or case.