Reddit reviews Discrete Mathematics and Its Applications

Rosen's Discrete Mathematics and Its Applications is the classic (which I haven't read), but if you want to avoid spending yet another $130 on a text, you might want to check out the Schaum's Outline of Discrete Math.

I have a few quibbles with the organization of the Schaum's. (I see no reason, for instance, why relations should be taught before Propositional Calculus and Boolean Algebra.) But it's a good resource, especially if you cover up the answers to the solved problems so you can get instant feedback on how well you understand the concepts.

But as a general rule, I wouldn't worry too much about Amazon ratings of textbooks. A lot of the ratings come from disgruntled students who hated the class, hated the teacher, and take their frustrations out on the textbook. You have to take these with a grain of salt.