$3000 is quite a lot of money, are you intending to use this computer for a long time? There's really no such thing as future proofing because technology just changes so quickly. I suggest saving some of that money and when the time comes where a new hardware has been released, you can upgrade that hardware only.
An example, there was a video card that was release around November 2007 which is about the best one at that time, and now 4-5 months later, that video card has been replaced by a better one with the same price as the November card. And new generations of video cards are coming out again.
Anyways, will you be needing a keyboard, mouse and monitor? Here's what I suggest then:
Update
EVGA 123-YW-E175-A1 LGA 775 NVIDIA nForce 750i FTW SLI ATX Intel Motherboard - Retail
Model #: 123-YW-E175-A1
Item #: N82E16813188026
Return Policy: Limited Non-Refundable 30-Day Return Policy
In Stock
$199.99 -$10.00 Instant $189.99
Update
XFX PVT88GYDD4 GeForce 8800GTS (G92) 512MB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready SLI Supported Video Card - Retail
Model #: PVT88GYDD4
Item #: N82E16814150267
Return Policy: Standard Return Policy
In Stock
Mail-in Rebate
$249.99 $249.99
Update
CORSAIR CMPSU-750TX 750W ATX12V / EPS12V Power Supply - Retail
Model #: CMPSU-750TX
Item #: N82E16817139006
Return Policy: Standard Return Policy
In Stock
Mail-in Rebate
$179.99 -$50.00 Instant $129.99
Update
Intel Core 2 Duo E8400 Wolfdale 3.0GHz LGA 775 65W Dual-Core Processor Model BX80570E8400 - Retail
Model #: BX80570E8400
Item #: N82E16819115037
Return Policy: Processors (CPUs) Return Policy
In Stock
$194.99 $194.99
Update
mushkin 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500) Dual Channel Kit Desktop Memory Model 996599 - Retail
Model #: 996599
Item #: N82E16820146785
Return Policy: Standard Return Policy
In Stock
Mail-in Rebate
$139.99 $139.99
Update
Seagate Barracuda 7200.11 ST3500320AS 500GB 7200 RPM SATA 3.0Gb/s Hard Drive - OEM
Model #: ST3500320AS
Item #: N82E16822148288
Return Policy: Limited 30-Day Return Policy
In Stock
$94.99 $94.99
Update
Pioneer 20X DVD±R DVD Burner Black SATA Model DVR-215DBK - OEM
Model #: DVR-215DBK
Item #: N82E16827129020
Return Policy: Standard Return Policy
In Stock
$30.99 $30.99
Update
Microsoft Windows Vista 64-Bit Home Premium for System Builders Single Pack DVD - OEM
Model #: 66I-00788
Item #: N82E16832116204
Return Policy: Software Return Policy
In Stock
$109.99 -$15.00 Instant $94.99
Subtotal: $1,125.92
You can get a better processor, a larger size hard drive (or more hard drives

) or go with 2 9800GTX if you really want to spend all that money.
Computer case is a personal preference, find one that you like and make sure its big enough for SLI (if you intend to do SLI).
Hope that helps,
Kamille