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.