G+ Community: Micro Maps
"..making dungeon maps on the tiniest medium possible. That's the only rule! Examples: - Post-It Notes - Tiny Bits of Paper - Matchbooks - Fingers - Fingernails - Tiny Notepads - Etc... If it's tiny and you can draw on it, it's micro!"
I think the results that people come up with are amazing, with such little space these folks cram amazing little dungeons or maps. Check out some samples: