Years ago, there was a Beavis & Butthead book out called "This Book Sucks." They had a two page section for instant band names. It worked simply as "pick a random word from Column A, Column B and Column C," or just use two of the columns.
Here's a site that automates it:
http://www.danbala.com/dirck/beavis/
Some of the things that come up are just retarded, but others actually sound decent.