You could do a "theme block" challenge -- each month, the theme is chosen for the next month (January - snowflakes; February - hearts/love; March - shamrocks, etc.). Each person makes 1 block, and at the next meeting, the blocks, with no identification for the maker, are placed on a table with a ballot box (can be a cup or paper bag) and ballots. Everyone in the group, whether they brought a block or not, votes for the block they like the best. The block with the most vote wins, and the maker of that block wins all the blocks.
I like the birthday block idea, and will suggest it to my guild.