I use Soywiki: http://danielchoi.com/software/soywiki.html

Toss something like this in your .bashrc or .zshrc to run it in MacVim and have an easy command:

  export SOYWIKI_VIM=mvim
  alias wiki='cd ~/wiki; soywiki'

Then just git init and push it up to a private GitHub repo, and you can check it and edit it on the go through the GitHub site.