Is there a reason you want SLI? I recommend you buy a single 8800GT card instead of 2 8600 cards in SLI. Unless you're playing 1900x1200 w/ max settings (16xAA / AF ) I don't think you'll see more than a 5-10% in FPS, and even then I think a single 8800GT will outperform.
What OS are you going for? If you aren't using a 64bit OS, then don't buy more than 2gigs of RAM. 32bit OS won't use recognize than 3.5gigs, sometimes it will recognize even less.
All that aside, I'll suggest some parts for you:
CPU-
E6750 $179.00-
http://www.newegg.com/Product/Product.aspx?Item=N82E16819115029
Core2Duo E6750@2.66Ghz benches pretty close to the Q6600 in gaming. If you want Quad core though... try this:
http://www.newegg.com/Product/Product.aspx?Item=N82E16819115017 Q6600@2.4Ghz $279.00. Go for the Quad if you've got the cash and want to future-proof your system a little more.
Motherboard-
Gigabyte P35-DS3R $129.00 - Good, stable motherboard. Good OC'er from what I hear.
NO SLI
or
Gigabyte P35-DS4 $177.99 - If you must have SLI, this is the way to go.
RAM-
2x1GB OCZ Platinum DDR2 PC6400 Dual Channel Kit (Cas 4) - $74.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16820227139
or if you want 4gigs you can try a Quad Channel kit (or just get 2x2GB) $141.99 -
http://www.newegg.com/Product/Product.aspx?Item=N82E16820227252
Video Card-
8800GT $269-309
If you can find it available anywhere
2x8600GT are about $109-149 / card, but I don't think they are the beset gaming cards... maybe someone that knows some decent ATI cards can pipe in.