I assume you are using source control? Add your references (binaries) to your solution and keep them stored locally, along with the source code.
By keeping everything together you can always go back to a particular version of the source and be able to build it, without having to worry about what binaries you were using at that time.
Also, this allows you to update the binaries once - then all the developers can just pull down the latest ones whenever they do a "get".
Edit: If you do this you also can just keep one copy of the dll which can be referenced by multiple projects in your solution.