For my own personal use: Probikekit.com, REI.com, and Pricepoint.com. All three are great in price and shipping time.

At work: The Hawley Co. Them guys can move product faster then anyone, especailly with DHL. I can order product at 4pm and have it one hand by 11am the next day. It does help I am 200 miles from their warehouse. Then there is Park Tool and Pedro's, both try and outdue one another with customer service.

My local LBS, Lowcountry Bicycles www.locobikes.com is awesome. Even though I worked there this past Christmas shopping season, they are great. Good inventory, experenced mechanics, and an in house wheelsmith that can tell Mavic a thing or two about wheel builds.

On the road I've had good experences at:
Andy Jordan's Bike Warehouse in Augusta, GA (caught a clothing sale and a great group ride)
Outspokin' in Augusta, GA (rented a bike)
Bicycle World in Florence, SC (quick fix before a century)
Ricardson's Bike Mart in Richardson, TX (rented a bike)