We use BugTracker.Net. It's an ASP.Net based system that is easy to configure, and easy to use. Our internal testers are generally not very tech adept, but they required almost no training for this. Another nice thing is that, being open-source and based on ASP.Net and SQL Server Express, .Net programmers will find it interesting to poke around the .aspx pages and SQL queries. The developer is good about answering questions on the forum and encourages users to modify the pages and queries if the built-in settings don't need their needs.