My app code is starting to get unmanageable and I want to start source control, primarily because I need to branch my code.
What are some good systems that you have
I vote for Git
You can set up a project at code.google.com, and use a source code repository provided by them. I think they offer Subversion and Mercurial as source control systems, and I use Subversion.
After you've got that set up, you can just use Subclipse to connect to the repository.
Besides all voting for git I'll vote for the following:
I would also vote for Git. I have little experience with Git and SVN, and I enjoyed Git more. It's fast, it's easy, i didn't have any problems with this. There's good Git repository service github.com, but setting up your own repository is very easy. But you can have some trouble with integrating it with Eclipse :(
If you are not working on a team and you just need version control for yourself, SourceGear Vault is free for a single user and they have a nice Eclipse plug-in.
I use it for Android development and it works like a charm.