1) Online games - turns out she's not much of a gamer (online puzzles, mazes, coloring games, etc. are liked, but not shoot-em-up, kill-the-alien-sum type games), so the free games on http://www.arcademicskillbuilders.com/ and other education game websites didn't do the job.
2) Addition fact songs scattered strategically throughout a newly-burned CD for car listening - dd3 now knows most of the addition facts, but dd6 must have already passed the stage where she memorizes every little thing she hears in passing. Most unfortunate.
3) Flashcards - moderately effective at reinforcing the sums she already knows and at giving me a chance to explain how to figure out other sums from the known ones, but kind of boring for both of us and so used only a few times.
4) We made 100 paper cutouts for the 0-9 sums in 10 different colors. I taped these on the kitchen wall and periodically ask her some of them. If she can answer one quickly, then I take it down. Over half are still hanging on the wall. Dd3 keeps answering my little pop quiz questions before dd6, which annoys me and probably frustrates dd6.
5) Cuisenaire rods - I pulled these out today and let her use them to show all the different ways to make sums up through 10. She enjoyed it, so maybe we'll use them again.
6) Addition Bingo game - dd6 enjoyed our Addition Bingo board game, but dd3 became temperamental and didn't want to play the game correctly, so I hesitate to get it out again. Same goes for Chutes and Ladders. (Ah, board game strife. When do they learn to cope with losing? Come to think of it, I still won't play Risk because I don't like that I never win....)
7) Various worksheets printed off from the internet and pages from sundry math workbooks - rather randomly chosen to keep her writing down math and reinforcing all the math that she has learned thus far.
We are stuck in our math worktext at the first page of double digit addition. I told dd6 a month ago that she needed to know her addition facts in order for her to learn double digit addition. She believed me, and now she absolutely refuses to work on double digit addition until she has memorized her sums. To tell the truth, I'm bored of working on 0-9 sums. But we'll keep at the task until it's mastered because it's truly fundamental. And because she won't let me move on.