The patterns and practices team come out with some fabulous stuff that I have used many times over the years and which I love pointing out to my customers, who usually haven't the time to keep up with everything that's coming out of Microsoft and so often haven't heard of some of the stuff that's available. They have things like the application blocks, which are compiled assemblies (plus source) you can use to solve common problems in your .NET applications, like logging, exception handling, caching and data access (there are more but those are the ones I have used the most). For Windows Forms programming (Smart Clients), there is also the Composite UI Application Block (CAB), which, if you are building a winforms application of any significance at all, then you should be using to base you program on.
Then, of course, there are the Software Factories - an advanced form of code generation (adding wizard-like guidance, documentation and finished examples of how to use the generated code). There are three currently available, for use when building WinForms (Smart Client) apps (upon the CAB, of course), Web Services and Mobile Clients (also built upon the CAB, but a subset of course.)
A new member of this list that you might want to take a look at is the Web Client Software Factory, which is intended to offer for the Web what the Smart Client Software Factory offers for the desktop - guidance and best practices on building Web Clients in the .NET world. It's still in alpha but there are weekly drops and it's moving fast so it's worth taking a look just in order to see what's coming, as you know it will save you some time... 🙂