We are using TFS and VS 2010.
I have been working on a project that is using TFS as source control. I have quite a few dlls that I have downloaded (such as log4net) and
Andy's suggestion is a good one and I've used that in the past. At my current job, we have a "reference" folder on a network share for all of us to build from. We have a very fast network here, though and all developers are in a single office. This solution won't work as well if you have a lot of remote developers or a slow network.