Really hard to beat Ebay. Find the parts you want and buy them from a trusted seller through there. That's usually a good place to go.
CamelCamelCamel.com tracks prices on Amazon to give you a better idea of sales.
Then use something like FatWallet or MyPoints (what I use) to get even more money back. Some credit cards have incentives through their site as well. My Chase card had an additional 5% back from Amazon during the holiday season.
If you really want to get good at saving money, hang out on Slickdeals.net and you'll learn a lot.
Have fun!
- Aaron
