Kevin Rose (@kevinrose), the founder of Digg, just released a beta version of WeFollow.com. We Follow is a user generated Twitter Directory that allows any Twitter user to tag themselves. To get started all you need to do is send a tweet to @wefollow. You can only place yourself into three categories at the moment. So to do this you would ad #categoryname to the post.
TIP: Just note, to create a multiple keyword category you will need to use the underscore (I do not think a lot of people use this - see socialmedia category). This could have better long term benefits since people will search by "social media" versus "socialmedia".