I'm also a Mantis user, and I'm quite happy with it.
Mantis supports Git and SVN integration, if you use the Source plugin. You can find detailed information on how to add these functionalities to Mantis at the following URL: http://leetcode.net/blog/2009/01/integrating-git-svn-with-ma...
Note: Importing repositories with a couple hundred commits will take a while!
I also like FlySpray, but unfortunately, the last commit seems to be 1 year old.