A common theme we've heard from our users is the desire to be able to work offline (in the "edit-merge-commit" style) when working on their CodePlex projects. Six months ago, we started working to write such a client that would integrate with our existing TFS server infrastructure, and today we've released our first beta of the client.
The CodePlex Client is a command line client for Windows, and requires .NET 2.0. The online documentation is available here.