I like sidewinder. Try to get most of my stuff from there unless the price is way different elsewhere, or don't have a particular item.
Last time they charged me $10 for shipping, then refunded me $5 cause they put it in a $5 USPS flat rate box. That was good business.
Other places listed in this thread have charged me like $13+ and it's arrived in a $10 flat rate box, leaving me thinking wtf? Hate it when shops try to make extra $ on shipping.
Ebay has some good items and some of these stores have ebay sites, but now that Bing is done it's no better, other than more protection and a feedback rating.
Microcenter also has the best B&M water cooling selection I've seen, little more expensive than online but if you need something quick it's good to have.