TeamSupport.com

Designed to be used by both the customer service and development groups, TeamSupport integrates a powerful help desk solution for the customer service department with a comprehensive bug tracking tool for the developers and QA departments.  

TeamSupport also has a rich "desktop-like" gui which makes the product quick to learn and easy to use.  

The first three users are free (with no strings!) which allows small teams to use a great tool for free and larger teams to evaluate the software risk free.

http://www.TeamSupport.com