The DotNetSlackers site has a nice series of articles about design patterns. The articles were written by Granville Barnett and are a very good read. Here is what is in the first four articles.

Design Patterns – Part 1
Learn how to design more robust and maintainable code by incorporating design patterns into your software projects.
1 Introduction
2 The strategy pattern
3 Implementing our design
4 Summary

Design Patterns – Part 2
In this part of the design patterns series we will take a look at the observer design pattern.
1 Introduction
2 What is the observer pattern?
3 The Design
4 Implementing our design
5 Aren’t events already in .NET?
6 Summary

Design Patterns – Part 3
In this part of the design patterns series we will take a look at the factory pattern.
1 Introduction
2 The simple factory
3 Factory pattern
4 Summary

Design Patterns – Part 4
In this part of the design patterns series we will look at the singleton pattern.
1 Introduction
2 How is a singleton typically implemented?
3 The static modifier
4 Issues with our first design
5 beforefieldinit
6 Summary
7 Acknowledgements
8 References

So what are you waiting for? Start reading the articles!