I thought I'd share my pick-thing-to-do-at-random app that helps somewhat. You just add things and then it shows you them at random. You can click to commit to do something for a while, or just flick to another thing if you can't do that now. I've added hundreds of both timewasters and productive activities there and it's quite cool to do this kind of lottery to determine what to do now.

Obviously it won't work if you just keep flicking until you happen upon a favorite timewaster, nor when you have something that needs to be done now. It's also essential to have clearly defined activities, even if it's just "think really hard about what to do about <whatever> and make that a new activity" or whatever. Tell me what you think.

http://things-be-done.appspot.com/ (google login needed for persistent storage, but you can play without logging in, data will be associated with a cookie left in your browser (and will be transferred once you do login))