http://www.tfproject.org/tfp/tilted-technology/150310-ultimate-gaming-computer.html thread is a nice template to go off of.
Look at this stuff:
COOLER MASTER COSMOS S RC-1100-KKN1-GP Black Aluminum ATX Full Tower Computer Case - Retail
Western Digital Caviar Black WD1001FALS 1TB 7200 RPM SATA 3.0Gb/s 3.5" Internal Hard Drives - OEM
EVGA 017-P3-1295-AR CO-OP Edition GeForce GTX 295 1792MB 896 (448 x 2)-bit DDR3 PCI Express 2.0 x16 HDCP Ready SLI Supported ... - Retail
Antec TruePower Quattro TPQ-1000 1000W Continuous Power ATX12V / EPS12V SLI Certified CrossFire Ready 80 PLUS BRONZE Certified ... - Retail
OCZ Gold 6GB (3 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Low Voltage Desktop Memory Model OCZ3G1600LV6GK - Retail
COOLER MASTER Intel Core i7 compatible V8 RR-UV8-XBU1-GP 120mm Rifle CPU Cooler - Retail
Intel X25-M SSDSA2MH080G1 80GB SATA II MLC Internal Solid state disk (SSD) - OEM
ASUS P6T6 WS Revolution LGA 1366 Intel X58 ATX Intel Motherboard - Retail
Intel Core i7 920 Nehalem 2.66GHz LGA 1366 130W Quad-Core Processor Model BX80601920 - Retail
LITE-ON Black 4X Blu-ray Reader SATA Model iHOS104-06 - OEM
LITE-ON 24X CD/DVD Burner Black SATA Model iHAS324-08 - Retail
That right there is just over $2,200 at newegg.
i7 is kick ass, no doubt. The motherboard can support 3-way sli (the power supply does not but I don't know if that is even possible with the 295). One limitation of the motherboard is that it only has 6 SATA slots.
I love the look of the cosmos case. If I could have afforded to spend $200 on a case that would be it. They have variants with windows or aluminum.
IMO, sli is great for upgrading because it can allow you to take advantage of what you already have but if you are starting from scratch you might as well go for 1 great card over two good cards. Someday the two good cards will be two shitty cards but the great card will still be good. At that point you can get a matching good card and be back on top again.
For an extra $120 you can upgrade the HDD to 2TB.
If you really want to go crazy and can go $300 over budget (what's an extra 12%?) you can swap the SSD for a regular 1TB drive and upgrade the processor to the i7 975. That is the top retail processor but it costs $700 more than the i7 920.