While Matt took the girls to a birthday party, I watched an episode of Weeds (season 2, a new addition to Netflix Watch Instant), and made flashcards using a Sharpie and 80 blank notecards. I wrote each number from 1-40 on one notecard, its number word on another notecard, stuck them back-to-back with a glue stick, laminated them, cut them out, and punched a hole in the top left corner of each one.
Now, every morning after Sydney tears a link off of her paper chain (it's quite fabulous, now that she's made her peace with it) and I tell her how many days there are until her birthday, I lay out maybe five of these flashcards, and Sydney finds the one that matches her number. Then I give her a fine-point dry erase marker and let her trace and draw on the flashcard for a while:
The plastic laminate allows the dry erase ink to be wiped off with a corner of dishtowel (or a sleeve, sigh).
When she's done playing, I give her the bookring, and she adds that flashcard to the others that she's collected. In 38 more days, she'll have the whole set!