newegg.com is one to check.
I also check pricewatch.com and pricegrabber.com. These two sites link to a lot of other sites that actually sell the products. Prices and shipping aren't always right, and there are some places that are not very good that they link to. If you use these sites, make sure that you check the feedback on the sites, and see what kind of feedback and how much feedback the site has received.