If you are looking for a great project to learn about ASP.NET, C# and Web Application Security, WebGoat .NET is a great place to start.
Please grab the code (here or here), read the current issues and join the mailing list
See my WebGoat.NET in Action (and how I set-it up) post if you need help setting it up.
And please fell free to invite others to join the party :)
Like I just did for this Reddit question
Where I answered