I like Tree Fort with their price matching service.
Nashbar is at the bottom of my list with their slow as a snail shipping.
Modern Bike is good as they are local and I can pick up my order in person if needed, although "in stock" to them does not mean the item is in their possession.
Art's Cycles has been a source for some good deals.
CRC, now part of the Wiggle-CRC Group has great service. A recent order left Northern Ireland on July 3, it was on my door step (in Iowa) July 5. Shipped free.