i work in asp.net 2005 c# sqlserver

i have heard about desing patters

which is the good book for that

Design Patterns: Elements of Reusable Object-Oriented Software (Addison-Wesley Professional Computing Series)

Design Patterns in C# (Software Patterns Series)

my favorite book

Patterns of Enterprise Application Architecture (The Addison-Wesley Signature Series) (Hardcover)

http://www.amazon.com/Enterprise-Application-Architecture-Addison-Wesley-Signature/dp/0321127420

This is a great introduction to the world of design patterns:

Head First Design Patterns
http://www.amazon.com/Head-First-Design-Patterns/dp/0596007124/ref=cm_srch_res_rpli_1

236 Amazon customers can't be wrong, it really is a joy to read.

Then when you have mastered the patterns see how you can refactor your code towards them:

Refactoring to Patterns
http://www.amazon.com/Refactoring-Patterns-Addison-Wesley-Signature-Kerievsky/dp/0321213351/ref=pd_sim_b_title_9