Great answers...the first question to ask is "Who is your audience?"
Like Rose_P says, miniatures do well for me. Granted they don't take much fabric...often I proclaim "and no yardage was harmed in the making of this quilt"...but they are time consuming. A recent donation quilt took me 12 hours just to do the background before I put the applique, embellishing, quilting and binding on...but it sold for $120. Well worth my time for a donation. And yes quilters who won't work this small...1/4" finished pieces...will buy.
This summer I made a college 62 x 82 quilt with a minky type backing. Silent auction brought $200..my costs $80. The 82" length is great for a dorm room.