You might want to take a look at Icon fonts. http://css-tricks.com/examples/IconFont/
EDIT: I'm using Font-Awesome on my latest project. You can even bootstrap it. Simply put this in your <head>
:
<link href="//netdna.bootstrapcdn.com/font-awesome/3.2.1/css/font-awesome.min.css" rel="stylesheet">
<!-- And if you want to support IE7, add this aswell -->
<link href="//netdna.bootstrapcdn.com/font-awesome/3.2.1/css/font-awesome-ie7.min.css" rel="stylesheet">
And then go ahead and add some icon-links like this:
<a class="icon-thumbs-up"></a>
Here's the full cheat sheet
--edit--
Font-Awesome uses different class names in the new version, probably because this makes the CSS files drastically smaller, and to avoid ambiguous css classes. So now you should use:
<a class="fa fa-thumbs-up"></a>
EDIT 2:
Just found out github also uses its own icon font: Octicons It's free to download. They also have some tips on how to create your very own icon fonts.