We are using Maven for a large build process (> 100 modules). We have been storing our external dependencies in source control, and using that to update a local repo.
You should use Artifactory
Its latest version was a real jump
You can backup incrementally your repositories , which means you can have all your artifacts saved and maintain
Its has a easy to use web ui
and is really easy to set up
i enjoyed it a lot
check out its new version 2.0