I'm most familiar with Trac (http://trac.edgewall.org/) which is web (python) based and haven't really run across any SVN source/bug tracking system that is as user-friendly. Whatever you do, stay away from SourceSafe
What about Bugzilla? I believe it's open source, it's certainly free and it can be used with various CVS systems SVN/GIT/VSS/Perforce etc...
Every company I've worked for has used it for tracking bugs, my previous employer used it with SVN(nice!) and VSS(blech!).
My current employers use it with Perforce(nice!).
From what I've heard (and judging by some of the rather explicit outbursts from our network administrators office), Bugzilla can be a bit fiddly to set up properly. But once it's up and running it's pretty solid!
MantisBT and Trac (as endorsed by ShawnCplus) are a couple of other popular bugtrackers. I believe Trac integrates quite easily (and rather well) with SVN.....Never used it, but heard good things about it!
Hope that's of some use to you.
Cheers for now,