This thread on Stack Overflow is useful if you want to broaden your C# skills by using features/idioms/techniques you may not yet even be aware of:
http://stackoverflow.com/questions/9033/hidden-features-of-c
The question is closed, but there are plenty of interesting answers.
One caveat: some idioms may seem really smart and/or terse, but others may have trouble understanding such code at at glance.