We are currently a HP house when it comes to printing. Most of are units are fairly heavy duty - eg Laserjet 9000's & 5500's. We use original products as we tried unbranded and refils and massive problems with our units. The ink was alot more sticky and therefore caused alot more paper jams.

The cheapest price I have seen branded toners are on ebay - not very consistent in terms of supply.

What kind of printing are you using your units for eg - brochure, art work, letters etc..
If you can do some analysis and determine you cost per page you may find out sourcing certain jobs may save you a significant amount of money.

Let me know if you need info as I have been through the exercise.

Regards
Parin