Personally, I like Tarsnap and anything from the OpenBSD project. Of course, this is highly subjective, and I would not call the code 'beautiful'. However, to me, these are a few examples of code performing complex tasks written in a simple, straight-forward way that I can follow and understand.
If you like the Tarsnap code, you should read the spiped code. Tarsnap is made ugly in places by needing to work with/around the original tar code it's based on; spiped is code entirely written by me.
