What are some recommendations?

I promised my 11 year old daughter that I would get her anything in ToysRus under $20 if she does well in school and she did. What are somethings you recommend for me to get her. She has a wii. She like to use the laptop to play games. She has a sister. She plays games that are causal but are really competitive. I want her to play more then stick to electronics. I need something under $20 dollars that would keep her busy and no tget bored with it! What do you recommend?