The popular Twitterverse by Brian Solis and JESS3 is busy, but interesting.
Jan Mirius has put together a one page view of the roles of different types of social media sites. Jan was an Icon Added Value / AVNA consultant for 8 years who is now founding a social media startup, uNapse. He is self described as having one leg in Munich, Germany and one in Brooklyn NY.
Cheskin Added Value put together a visual framework to explain the different functions of social computing last year, and then layered a few sites on top.
We also put together a framework to categorize social search sites.