The Bearhug is a tonally transparent, ultra-quiet, tiny, and easy-to-build compressor. It occupies some middle ground between the ultra-subtle compressors like the Flatline/Afterlife and Orange Squeezer and the super squishy compressors like the Ross.
For more info on the design, Jon goes into detail in this thread on DIYSB.
I built this one last night and it's everything Jon says it is. Very subtle, and a little bit of volume boost if you want it. Here's a few pics of my build.