Here's a small list that I've comprised and usually visit. Please feel free to add and share.
www.eastbay.com - The most mainstream site. Retail prices and selection. Very reliable service. Pretty much a sister company of Footlocker and Champs
pickyourshoes.com - This is my favorite site. Prices are pretty steep but they carry a good selection with rare models. Always updated.
23isback.com - Selection is very limited, but they have a release date section. Always updated. This is where I primarily source my info and post pics from.
designerathletics.com - Decent selection but very affordable. Some shoes are rare and even hard to find on mainstream sites.
instyleshoes.com - This used to be my favorite site. They used to update it alot. Very expensive and usually out of stock. I once ordered a pair of Jordan XI in cool grey. I lucked out and they forgot to charge me.
uptempoair.com - Very good selection and great prices. Sometimes they have availability before release dates.
If you can add more, please do so and share. Let's keep this mini sneaker community going.