Back when I used to have an MSDN license, or work for a small enough company where I administered the license, I always enjoyed receiving the various Microsoft posters.  I had posters of all of the .Net System namespaces, ASCII posters, etc.  A really useful one was the keyboard shortcut poster.  Scott Guthrie just posted the new Visual Studio 2010 keyboard shortcuts posters.  Using even a few of the most productive keys will make you day coding much more enjoyable.  I encourage all programmers to pick up a copy of these posters and pick up a few new key combos.

I just stumbled across the new System.Collections.Concurrent Namespace in .Net 4.0.  I needed a thread safe dictionary and a coworker suggested I check out ConcurrentDictionary.  Of course if you are attempting multiple operations against the dictionary you still need to lock or use some other type of mutex.  But if all you are doing is reading a writing from multiple threads in single, atomic statements then this is the critter for you.