Comparing VCS
A comparison of some of the open source distributed Version Control Systems.
Not sure why SVN was included in this comparison, since SVN is NOT a distributed VCS. However, there is a wrapper around SVN (called SVK) that adds distributed features if you want to move to a distributed model but still retain SVN repos at the core.
Distributed v. Centralized VCS
Linus really emphasizes Distributed Version Control Systems (video) and thinks anything else is insane, brain damaged, ugly and stupid).
Obviously centralized systems have been used for years, but one of the many points he makes is that centralized systems only work well in a tightly controlled environment in a single location. Linus did something to meet his needs: he created GIT
Distributed VCS
There is wp:BitKeeper but that is a commercial product