The "Methode de Batterie" series of books by Dante Agostini are well known by drummers as a comprehensive method for the kit. Check out volume IV for a number pages of polyrhythms that can also be used by other musicians. There are two part exercises that can be played between the hands. They start progressively with 16th and 8th notes, and then explore 2 against 3, and 3 against 4. Although I have not reached the end yet, I have found this a very systematic and practical method, which followed step by step helps to learn these rhythms thoroughly.