If you're using Jekyll, add the category_list.rb file to your _plugins directory. This will give you the helper category_list. In your views, you can use this function to print out a list of categories:
{% category_list %}
Then copy or include the category_list.css styles into your project. The list looks something like this:
Where personal is the hover state.
Feel free to send pull requests, steal the code, claim it as your own. I'd appreciate feedback on how I could improve the Ruby or CSS.