I love sketching out ideas for new games and making paper designs. I also love seeing other people's designs (Ever since I first read "The Art of Star Wars" I got bit by the concept art bug)
Obviously the guys at http://gamestorm.tumblr.com/ love these too and are showcasing the "napkin doodles" of game developers.
It's fun and inspiring stuff - always great to see the creative mind at work! Who knows, you might see one or two of my designs up there one day!