Sociable 2.0 has just been released.  I’ve tried other social bookmarking plugins, but I think this one is the best.  It’s easy to install and has a good interface.  For some reason it didn’t work automatically in my posts, and I had to put the line of code in manually, but I think this has more to do with the theme I’m using than the plugin itself. It supports all of the major (and most of the minor) sites.  Click on one if the icons below to try it out!