What instrument(s) are you concentrating on?
From my days of preparing to teach violin, Ayola's _Winning Rhythms_ is an excellent (if somewhat cutesy and childish) book for learning rhythm/counting from the very simple (quarter/half/whole notes) to very complex syncopated rhythms. The _All For Strings_ series is fairly good for beginners; the first book or so will cover basics from holding the instrument properly and reading notes to somewhat more advanced material such as basic double stops and shifting to third position. The _Suzuki_ series is wonderful, but really belongs with lessons and a good teacher.
The basics of reading music are very simple; the hard part is applying the knowledge to real life (ie, sightreading and ensemble playing).
~Ladi