I am a whole "in the car curriculum" that can be useful to slip some learning in: http://teachingmybabytoread.blog.com/classical-education/in-the-car-curriculum/

Another fun game to play is Magic Word: http://teachingmybabytoread.blog.com/2011/03/03/magic-word/

This summer my son is also working on Right Start level D for math:http://teachingmybabytoread.blog.com/2011/07/12/right-start-level-d/

Good luck to you!