gmpartsdirect.com is good as well. I've never been able to beat their prices for dealer parts, even when shipping is factored in. I usually submit the customer service form when I'm looking for a part. You just need the VIN (should be on the vehicle registration), your e-mail and the part you're looking for. They'll get back within a couple days usually. They also have a catalog, but it's a little clunky and somewhat less than complete.