I've stumbled upon a great web resource containing description of design
patterns, antipatterns and refactoring techniques. It is easy to read, have
good illustrations and intuitive navigation. I would advice visiting it.
Design patterns are described in GOF style and there are mainly (if not
only) GOF patterns. So in case you haven't this great book on your shelf when
you need it, you can go to this website and find info you need. In addition to
design patterns there is good description of antipatterns and refactoring how-to’s.
Code examples on this site are in C++ and Java, but it should be easy to understand them if you are proficient in C# only.
I almost forgot to leave the URL :-) Here it is: http://sourcemaking.com/