4870 from Sapphire or PowerColor?

Newegg is great, but I'd head to ZZF for a 1GB 4870. Just came back in stock for $120 shipped (after $20 rebate)
http://www.zipzoomfly.com/jsp/Prod [...] e=10010111

edit: To answer your question, I've had good luck with both Sapphire and Powercolor, so personally I'd go with the $25 cheaper model.

Check the Newegg reviews: I think Powercolors customer service is quite poor, importaint with a new piece of hardware.
If the case this build is going in is small, cramped or lacks good airflow, those two cards could easily cause heating issues because neither exhausts its heat out of the case and this would be a better choice:

http://www.newegg.com/Product/Prod [...] 6814125225

I know you're on a tight budget but I strongly advise looking into either a GTX260 or 1Gb HD4870; 512Mb is getting small for modern games and, even at 1280x1024 some games already benefit from the larger framebuffers these cards offer.