Here are some of my group's past challenges:
Ugly Fabric Challenge - we picked a bolt of the ugliest fabric we could find. Picking out fabric was a challenge in itself, since we have such a wide variety of tastes and preferences in my group! But we finally found one that NONE of us liked. The only rules for the challenge were you couldn't cut it up so small that it was unrecognizable; the quilt was to have a perimeter of at least 48" and no more than 250"; and it had to be finished, i.e. quilted and bound. The goal was to force us out of our comfort zones. We had some awesome, awesome quilts that year, and not a single one was like any other! A very successful challenge. You can actually see the "ugly" fabric we used here:
http://www.quiltingboard.com/main-f1...c-t278770.html
Paint Chip Challenge - put several paint chips in a paper bag and each person draws one chip. Whatever color you pulled out of the bag was the color of fabric you had to work with, plus one other
fabric of your choice. I got lucky - I drew a paint chip called "tobacco", which was a soft grayish-beige. At first I thought it was horrid, but then I realized it was a blessing because it was so neutral. And then I got smart with my secondary fabric, I paired it with a lovely purple ombre that went from dark purple to pale lavender.
Shape Challenge - We made a list of 8 shapes - circle, square, rectangle, triangle, oval, hexagon, octagon, diamond. You had to use 3 of these shapes in the quilt, the shapes had to be identifiable. I appliqued squares onto the background in a circle, like numbers on a clock. Then I quilted triangles all over it. That one was a lot of fun, too!