A List Apart has an article about using Subversion to help with collaboration, especially with contract workers. Though there are some superior version control systems mentioned in the comments, like git, mercurial, or bazaar, they don not have the client support that Subversion has as of now. I especially use the Subclipse plugin for Eclipse for my work and checking code in and out of Subversion is a quick right-click away.
More importantly, how much client support for Subversion there is makes it easier to get other developers on board using it1.
The article also makes mention of Warehouse, which looks really interesting. I've used ViewVC in the past, but that does not help with administrating of the repositories, especially users and permissions.