Whats up Angus (beef?) Welcome to the forum.
Thats a good MB, I think the gigabyte GIGABYTE GA-EP45-UD3P with CORSAIR CMPSU-850TX, is a better deal, that combo deal with the 850W Corsair PSU is pretty sweet with the rebates and discount. That Asus board is okay to get, but the gigabyte seems to have a far higher satisfaction rating, if you want the Asus board get the combo with the CPU ASUS P5Q-E with Q9550, getting the Q9650 is a waste really and you save $50, they are the same cpu really and will OC the same amount.
Even though ATI supposedly has crossfire working well, I would just jump on this awesome deal for this 4870 ASUS EAH4870 DK TOP, $150 AR. Going crossfire depends on how high of a resolution you want to game at, if its around 1920x1200 then I'd say yeah, but most of us don't do that. You can always add a second card later if you get a hi-res monitor. If you wanted to have some fun with crossfire and not spend too much, I would do 2 4830 cards, that will beat a 4870 by about 30%, that would easily last you till the next generation of goodies comes out, and the 4830 cards would retain a lot of their value to sell off on ebay. The deals for a 4870 will pop in and out on newegg, this deal will probably be gone after tonight.
If you want to OC, then check out the performance of the coolers at: frostytech, you can see that the tuniq tower 120 has been knocked off its thron a while back now. Keep in mind that noise is just as important as cooling performance, too bad the "Akasa Nero AK967" isn't widely available, the "Xigmatek HDT-S1284EE" is another top choice. The TRUE is another good choice if teamed up with a quiet fan, Thermalright Ultra-120 Extreme, a good fan like a Yate Loon, get the 70cfm or 88cfm model, 70 is probably enough air flow.
For the ram, you don't have to spend a lot for performance. I would go for these G.SKILL PI Black 4GB for $55. If you want a high fsb, then just loosen the timmings to 5-5-5-15.