Am I correct by assuming that you're going to be using your computer for gaming?
Intel Core i5 750- $199 USD
G.Skill Ripjaws or Corsair XMS3 Memory 2x2GB Kit - $110 USD (approx.)
Gigabyte P55A-UD4 - 8x/8x CrossFireX support, although if you do use the USB 3.0/SATA III on the board, CFX will be disabled and the first lane will run at 8x - $189
or, if you're going to be serious with CrossFire, 2/3+ cards (No USB 3.0/SATA III): Asus P7P55 WS Supercomputer - $249
Cooler Master Silent Pro M850 850W - Enough for HD 4890s in trifire, modular, what more to ask for? - $160
or, if you're only going to use two HD 4890s: Corsair HX650 Modular PSU - $140
Case: Anything here really, I suggest the Cooler Master HAF 922 for $109, really nice case.
If you want a slightly fancier, but really nice case as well, the Silverstone Fortress FT01 is pretty good too, for $200.
Much thanks, 1 question though: That motherboard with max speed x8, does that mean half the speed I would get at 16x?
You will get x16 if you use a single video card and x8 x8 on Crossfire in 1156 boards. But I don't think you need to be concerned about crossfiring since the single HD4890 should be more than enough to play at the 1680 x 1050 resolution your monitor supports so Obsidian's recommendation with single PCIe Slot motherboard is a good one.
Thank you for all your input, especially obsidian86.
The I5 system will be more then enough power for gaming and just about anything else. But If you are into encodeing videos and 3d rendering then the I7 would be the better choice. I picked a pretty big PSU since you said you might do crossfire and will also ensure having plenty of power for future upgrade. If you plan on staying single GPU you could go to a 550 or 650 watt PSU but I would go for the bigger one for future add ons and upgrades. Now I saw an AMD system they listed in a previous post yea that will save you maybe 150 but it will not perform as well as an I5 750.
The I5 will overclock better, run cooler and perform better.