Clam (GitHub: sjl / clam.vim, License: MIT/X11) by Steve Losh makes running shell commands on buffers extremely convenient. He's made a screencast of Clam so you can see how to use it, but basically buffers can be piped through shell commands and the contents replaced.
It doesn't sound revolutionary, but the screencast sold me on it.
Gist.vim (GitHub: mattn / gist-vim, License: BSD) by Yasuhiro Matsumoto makes creating GitHub Gists extremely easy. Typing
:Gist will create a Gist with the current buffer; private Gists can be created by adding the
Gists can also be listed, fetched, forked, and otherwise manipulated. Yasuhiro has included lots of examples in both the project's readme and the plugin's documentation.