10 lessons in productivity and brainstorming from The Beatles is a great blog post by Tom Whitwell.
I remember Russell and I did number eight once, "Pretend to be someone else". We got stuck coming up with some ads so we simply pretended to be all the other agencies and imagined what they would do for the brief. What would BBH do? What would Mother do? And so on. So and so would have a singing dog. Such and such would shoot on a drone with a manifesto type voiceover. Thingy would use that trendy actor. We did about 7 or 8 agencies.
That was a fun hour. And it genuinely helped I think.