Trello uses an icon font and so can you
We use icon fonts on my current side project and it is wonderful to work with. We use font awesome (<a href="http://fortawesome.github.com/Font-Awesome/" rel="nofollow">http://fortawesome.github.com/Font-Awesome/</a>) which works well with (or without) twitter bootstrap.<p>It had greatly improved our UI and sped up development.