It's not uncommon for designers to set themselves challenges, we've covered a couple of them before here on UltraLinx. A former Facebook designer, Ben Barry embarked on a 100 days project that saw him creating patterns as a daily creative ritual. His creations are great, and it's crazy to see how he created such unique, interesting patterns on such a consistent basis.
The rules for Ben's project were simple; three colours and the one inch square unit as his pattern tile. He was also allowed to rotate the pattern tile but not mirror it or alter it any other way. The project has resulted in a book featuring all 100 of his created patterns, printed by Hemlock Printers. You can see all his patterns on his tumblr.