To encourage the girls to read, we've been keeping track of the books they've finished with a reading tree. We write Danya's books on the leaves and Gloria's books on the flowers. These are books they've read entirely by themselves. Danya's had to be chapter books.
Once Gloria finished reading 30 very easy reader books and Danya completed 20 chapter books we gave them each a surprise. They got playdough tools that we found at a teacher supply store. Each pack had a rolling pin, beveled pizza cutter, and other neat little toys for making shapes and patterns with their playdough. The girls really seemed to like them.
Now that their tree is complete we're discussing options for the next thing to hang on their door. We might do a reading train, with each book title written on a piece of the train or possibly a race track with titles written on cars.