I personally open a (yellow) phone book to a random page and brainstorm ways to make that particular industry more efficient. But then again I'm an efficiency consultant.

I'd peruse idea/complaint websites and see if one idea tickles your fancy:

http://www.sixmonthmba.com/2009/02/999ideas.html http://www.whynot.net/ http://www.quirky.com/ http://logolalia.com/ideafactory/ http://mybiggestcomplaint.com/ http://www.ilovetocomplain.com/