I ordered the HP Color Laserjet 1600/2600n Compatible Black Laser Toner Cartridge (Q6000A) from InkJetSuperstore.com. 

I was very pleased with the huge selection, quick & free shipping and the overall quality of the checkout.  The savings was over 40% from retail.  My final price was $53.99 and the retail is $85.99.

If you need HP LaserJet 2600 (color) laser toner refills or color laser toner, this would be one company I would recommend.