I've worked with GForge in the past:
gforge.org/gf/
(free for light use)
and Savane:
gna.org/projects/savane
(free free)
( also see savannah.gnu.org/ )
They're both based on the same code base as SourceForge, so are similar.
GForge was slightly more fancy when I used it, probably due to it being a commercial product, but Savane is fine.
RT is also very well regarded and deserves a mention:
bestpractical.com/rt
It can be a powerful too if set up well, although I've seen some messy installations.
This page has a good list if you would like to go shopping:
http://en.wikipedia.org/wiki/Comparison_of_issue_tracking_systems
I note you want to interface with subversion.
When I had to help get a small project up and running quickly in a recent contract we agreed to use git for our source control, and I found that we could host it for free at www.projectlocker.com/ which was just what we needed to cover our needs.
(5 users, a small directory of files and the bug tracking etc we needed around it) although I wouldn't recommend that for a long-term solution.
We were only ever going to be coding a one-off utility over the space of 3 months, and there were only 3 of us committing code.
Project locker supports subversion as well as git, in fact svn is their default.
It was very convenient in that we didn't have to do any installing or setting up ourselves, we just signed up and it was ready to use. One of the strongest points for us was the fact that my colleague could commit from Turkey, I could commit from home in the UK, and when we got together in the office in the UK we could access and commit to the same repository and bug-tracking from there as well. We could interface with it both from the command line via ssh, and via the web.
It was important to us that the repository was hosted for free and was allowed to be private, because due to the nature of the project being for a customer who would end up owning the code, the work we were creating wasn't open source.
github.com offers similar for a low price.