I'm re-reading the “Gang of Four's” book “Design Patterns” by Addison Wesley publishers. It has been about 4 years. I did not realize how monumental this book has been in my career the last few years. When I read through it a few years ago, I admit it blew me away. Meaning, I had trouble getting a grip on it. But now with 3 years of working with .NET it now makes great sense. I'm surprised how much I have actually used its knowledge.
Do yourself a favor and go get a copy of this book. ISBN = 0201633612.