Start a file somewhere (we did Google Docs) or even just a text file, and write down names as they come to you. Then after a few weeks, just look through the list (you will get ideas for new ones since there is a collection to look through).

To get started, this is also cool http://wordoid.com/

I've also used Mechanical Turk (have the job to submit 10 names, that doesn't have the .com still available for example).