The main suppliers of my habit are:
Newegg
Mwave
Googlegear (while their shipping is a little high, their prices are often better than Newegg and Mwave. AND they have a larger stock than both)
Techonweb (GREAT prices on some printers and Antec cases)
Ibuydig (For GREAT prices on Digital Cameras)
When these fail to have exactly what I want, some good backups are:
Comp-U-Plus
MicroX-press
Provantage