Obviously its a little higher than your budget, but you can fix this by dropping down to a smaller video card. It depends on your level of gaming. The HD4850 would be a good second choice and would save you about 50 bucks, bringing you within your budget.
However, I did not look for combo deals, and free shipping deals, just benchmark products that would suit you well, im am confident that with a little time you could get all these products at newegg within your budget through combo deals and whatnot.
Edit: If you dropping down to a HD4850, you could also go with a lower wattage PSU, like the Antec EA500, saving you some more money there.
Yea I just put down the core components, no paripheals, Getting an Xfire board would stretch your budget a little bit, because not only would the mobo cost more, but you would need to have an adequate PSU. Xfiring 2 HD4850 would be fine with the PSU I linked above, the 650TX, however if you were to get an HD4870 now, you would need to step up the PSU if you want to xfire.
You would not notice the difference in games, because at this point its still clock speed > # of cores (with a couple exceptions)
The monitor would be fine, I tried to find a cheaper monitor at that resolution, but didn't see one, so I must have missed that one you linked, but those are two fine changes, and helps with the budget =)
CORSAIR CMPSU-650TX 650W ATX12V / EPS12V SLI Ready CrossFire Ready 80 PLUS Certified Active PFC Compatible with Core i7 ... - Retail
SAPPHIRE 100258-1GHDMI Radeon HD 4850 1GB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card - Retail http://www.newegg.com/Product/ComboDealDetails.aspx?Ite...
OCZ Reaper HPC 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Dual Channel Kit Desktop Memory Model OCZ3RPR16004GK - Retail
AMD Phenom II X3 720 2.8GHz Socket AM3 95W Triple-Core Black Processor Model HDZ720WFGIBOX - Retail http://www.newegg.com/Product/ComboDealDetails.aspx?Ite...
Total shipped $795.80. Use this promo code to save another $10. EMCLWNW27
That being said, if you're happy with a 19" monitor at 1680X1050, you will have absolutely no need for another 4850. A single card will get you medium to high or better. In which case you can save money by going with a single PCIe mobo, and a less expensive PSU will meet your power requirements.