InkGrabber.com is traditionally a great place to find all the major brands of inkjet, toner cartridges and ribbons at very competitive prices.
They basically are up to about 85% off the retail prices for the cartridges, and one of the best things they do is put a promo code right on the front page to announce any sales. Inkgrabber.com is a clean, clear site, with an easy navigation to the major brands of copier/ printers, and most of the smaller ones as well.