I've had some folks who have attended my Design Patterns session suggest some links that they have found useful. (And if you want to check out the session materials, just go to my website: Learn the Lingo: Design Patterns.)
Head First Labs - Head First Design Patterns
This is the link for the "Head First Design Patterns" book that I've recommended. And there's some really good news. I noted that the book is written with Java samples, but that it's not too hard for a C# developer to follow along. The good news is that the labs includes a link to a collection of C# samples. Just search for "C#" on the labs page, and you should find it.
Head First Design Patterns Study Group
The O'Reilly On Java website has suggestions on forming your own study group based on Head First Design Patterns. I've heard from some folks who have done this, and they found that it was a good learning experience for everyone involved. Discussion with other developers usually leads to new insights for everyone.
Do Factory - Design Pattern Framework 4
This site sells a product called Design Pattern Framework 4. As a disclaimer, I have not actually used this product, nor do I really know much about this. But I have received recommendations from session attendees, so it may be something worth looking into further. In going through the information, there is also an endorsement from Miguel Castro (who is one of the big players in the .NET community), so that leads me into wanting to look at this a little more closely.
If you've had experiences with either the Head First Design Patterns study group or using the Design Pattern Framework 4, please drop me a line and let me know what you think.