»yahoo«

From their site:

"We'll be inviting 500 developers to attend the event, which will begin with hack-related presentations from some of the Web's most respected developers. We will then dive into 24 hours of hacking on a very nice collection of tools, APIs, and data, and end with awards from the sponsors plus bragging rights until the end of eternity or the next Hack Day, whichever comes first."

Now I have to thing about what kind of hack will be my part...

http://hackday.org/

Until today, the Yahoo APIs were available only for non-commercial use unless you applied for an exception. The concept of commercial and non-commercial has gone away and exceptions are no longer necessary in most cases.

You can now build Mashups and use our Maps for personal or business use as long as the applications are free of charge and under the rate limit, link to Yahoo! Maps or Driving Directions to your heart’s content or include advertising on the same page or site where you display Yahoo! Maps.

... Yahoo! Maps: You don't have to ask!

Yahoo released its Audio Search that includes audio from and information about a wide range of audio publishers. It looks across a collection of online music services (e.g., iTunes, Yahoo! Music Unlimited, Garageband.com) and audio files on the Web and lists all places where you can download specific files.

... http://audio.search.yahoo.com/