Design Pattern Summary Page

This is a nifty little explanation of each Design Pattern for C#

http://www.dofactory.com/Patterns/Patterns.aspx

An old collegue of mine had a much simpler summary of the GoF book here

http://www.jameswilliams.com.au/

Edit: Here is yet another page which has nice descriptions of each pattern.

http://sourcemaking.com/design_patterns