$180+ million opening weekend - calling it now. You've got the coolest super hero franchise, sequel to a huge hit, great cast and crew, and Heath Ledger's last performance. Thank god Spiderman 3 will finally be topped; that movie was horrible.
Don't buy an 8800GT unless it's like $150 or so. I don't know if Nvidia dropped the price on them like they did their 9800s, but it doesn't seem that way by current prices. You can get 9800GTXs and ATI's 4850 for around two hundred with the 4850 offering slightly better performance (I'd definitely recommend saving up an extra wad of cash for the 4850 if you were thinking of the 8800GT) . If you're buying now then I'd recommend an X38 board if you can afford it or a cheap P35 if you're on a more strict budget. If you want to SLI eventually then the 750i would be the chipset to go for. Of course you have plenty of time until D3, so you could just wait and see what technology has birthed by then.