If you like dancing Wii Just Dance games are a lot of fun. They get my kids moving too! I do it almost every evening. When it's fun, I'm less likely to quit. I plan to alternate with my Wii Fit board and program. Variety make for less boredom.
I just bought Wii Just Dance 2 for $50 (not cheap, but worth it in my opinion! ). According to the instructions, you can buy more songs with Wii Points. (I haven't done that yet.)