I recommend Susanna Epp's Discrete Mathematics with Applications, which I recently taught a university course out of quite successfully. It offers a gentle but

I recommend Susanna Epp's Discrete Mathematics with Applications, which I recently taught a university course out of quite successfully. It offers a gentle but rigorous introduction to proofs, logic, and combinatorics, with applications to CS. Useful exercises too. It is squarely targeted at beginners, if you know the stuff already then many other commenters have recommended more advanced books.