Back in the distant days of 2005, I stumbled across Dave's Random Premise Generator. From that I spun off dozens of concepts for one-shots. That page is long since gone (2012 near as I can tell), and the list of premises went walkabout last year, so I've built something like it that I hope to use to the same purpose.
Note: Since originally creating this page, I’ve made a python script that now posts these directly to twitter about one every half hour. So if you enjoy the Premises this produces, check us out on twitter @PremiseRandom