We've had a lot of success with Redmine for our community plugin development portal and I would definitely recommend it.
The community is very mature - especially the developer component. They take plugin development and maintenance very seriously and the standards have been consistently high (in our experience).
Plugs into both git and SVN seamlessly.
We also looked at trac. It was good, also had a had a well sized community, but lacked a certain finesse and polish. For us, usability was very important. We wanted to turn our Redmine into a portal not just for our community developers to code and share but also for our customers to browse the community plugins and apps that are available, in kind of like an 'app store' style interface. We pulled that off with reasonable success