Have you checked CodePlex??
CodePlex is not a new story ... we all already know about it that it is Microsoft's open source project hosting site. Developer from around the world can host their project and source codes. Surprisingly, a number of interesting projects are up and can be useful for anyone.
If you are thinking to start a new project, or looking for some good third party functionality or for nothing but just take a look of it and I am sure you will find pretty good utilities for your project.
I found following very interesting and/or useful projects: