I don't know if you mean $3000 American or Canadian or whatnot, but you don't need that much to build an awesome gaming computer. First, I would advise you to decide if you want to spend all $3000, or save money if you think you are safisfied with a good Gaming Computer (and in most cases, it's pointless to build the "Best" gaming computer).
These are 2 Specs that I recommend:
First, Decent and Money Saving Option.
CPU: Intel Dual core 3.0GHz speed and up.
RAM: DDR3 SDRAM with 1333MHz speed and 6GB space (get more speed and space if you want to, but that would pretty much be enough).
GPU: Nvidia GTX 285, GTX 295, ATI Radeon HD 4870 and Dual HD 4870.
HDD: 7200 RPM Conventional SSD however amount of space you would like.
Power: You would need sufficient amount of Power Outlet so around 800-850 Watt range.
Cooler: Standard Air Cooler or Liquid Cooling for more cash.
Second, Pure Performance.
CPU: Intel i7 Quad core processor with 3.0 GHz speed (approx $500 more than the previous option with Dual cores).
RAM: 1333MHz, 1600MHz or higher DDR3 SDRAM with 6-8GB memory.
GPU: Dual GTX 285, Dual GTX 295 and Dual HD 4870 Crossfire.
HDD: 10000 RPM conventional HDD or 256GB or 512GB SSD (if the budget allows)
Power: You would need sufficient amount of Power Outlet so around 950-1100 Watt range.
Cooling: Liquid Cooling.
You should choose this options at Gaming Computer Brands such as Ava Direct, Cyberpower or iBuyPower for good Price-to-Performance ratios.
For more info on choosing Gaming Computers, visit my site:
www.gamputer.com
Now would be a terrible time to buy dual 4870s; especially with this budget.
The 5870s are coming out very soon (this month) and from what I've seen, 1x 5870 would probably outperform dual 4870s in crossfire.
My suggestions:
CPU: Core i7 920+ (not sure what he was talking about $500 more, only the i7 975 extreme edition could possibly be that much more... the i7 950 is only ~$570)
CPU HSF: TRUE Black eXtreme or TRUE Copper eXtreme (beware, the copper weighs a TON and needs extra support)
Mobo: Any good x58
GPU: Radeon HD 5870 (coming out later this month)
RAM: 6GB or 9GB DDR3 1600 tri-channel SDRAM
PSU: at LEAST 850W; to be safe maybe a 1000W; especially if you plan a crossfire / SLI setup
pass on 10K RPM harddrives; go 15K or set up a RAID array with 7200RPM drives; OR go all out and get a SSD drive
put the extra money into a huge monitor, a nice case, maybe liquid cooling system?