We now have a Digg API profile in our ProgrammableWeb directory.
It's a good looking API. One of the interesting API design decisions they've made is that although they require an application key for all requests, as they note here: "The value of the appkey argument is up to you, within the constraints described below. Digg does not issue or authenticate appkeys at this time. It is used only for statistical purposes...The value of the appkey argument must be a valid URI (see IETF RFC 2396) that identifies the application making the request."
They also offer tookits for Flash and PHP.
In addition they're launching a contest "for the most creative and innovative visualizations and applications developed by our community using the API and Flash toolkit. All of the top 10 finalists will get prizes, with a Grand Prize featuring a Falcon Northwest gaming PC, the full catalog of EA PC games, and the Adobe CS3 Master Collection." This contest has been added to our ProgrammableWeb Contests page.
As Kevin suggests, "Digg on".