* Amazon.com: You can find the cheapest new equipment there. Just make sure to pick a reputable seller.
* B&H Photo & Video (http://www.bhphotovideo.com): Price is not the cheapest (but no sales tax); it's a long-time reputable source.
* Adorama Camera (http://www.adorama.com): Same as B&H.
* Costco Online (http://www.costco.com) or Local: Price is not great (plus sales tax and shipping), but return policy is unmatched. Good if you're undecided, and just want to try the camera out.
*Never* buy from your local Fry's Electronics or those from the malls (except small accessories that you can't wait to shipped to you from New York or wherever)!
If buying used:
* Craigslist (http://www.craigslist.org): Probably the cheapest local flea market out there. You can inspect the merchandise before purchasing. However, be careful. Buyer beware.
* Amazon.com: Very cheap. Just be careful, since you can't inspect the merchandise before buying.
* eBay (http://www.ebay.com): Same as Amazon.com.
* If you're adventurous, you can try garage sales, pawn shops, etc.