I run a small web start-up (5 people). Can anybody recommend a light-weight bug tracking database for us?

We do not want to spend a lot of money on this. Our project is not open source. We use CVS to manage our code base.

Clearcase, Jira, or better develop it yourself, you can post your requirement at website like http://www.getafreelnacer.com/ and let many web developers bid for your project and then you can hire whoever you like .