Algebra by "Mac Lane & Birkhoff" was my favorite textbook in college. Really thorough and not quite as dry as Dummit.

(https://www.amazon.com/Algebra-Chelsea-Publishing-Saunders-L...)

Mac Lane was also the father of category theory.

The freely available [1] is a nice supplement to some of the material in Concrete Mathematics, and this [2] is an approachable introduction to graph theory with side notes on both proof techniques and algorithms.

More generally, if you're not already comfortable with linear algebra (a couple college semesters "or equivalent experience"), I'd recommend both [3] and [4] for two entirely different perspectives. For modern algebra more generally, I'm a huge fan of [5].

If I could only take one introductory mathematics book to a desert island, I'd cheat a bit and take [6], [7], and [8]. While never directly involved in CS, Courant was very interested in the practical applications of theoretical mathematics, see, e.g., [9] and, well, most everything else he wrote.

I could go on and on, so I'll stop here.

[1] http://www.math.upenn.edu/~wilf/DownldGF.html [2] http://www.amazon.com/Graph-Theory-Graduate-Texts-Mathematic... [3] http://www.amazon.com/Linear-Algebra-Applications-Gilbert-St... [4] http://www.amazon.com/Finite-Dimensional-Vector-Spaces-P-R-H... [5] http://www.amazon.com/Algebra-Chelsea-Publishing-Saunders-La... [6] http://www.amazon.com/Introduction-Calculus-Analysis-Classic... [7] http://www.amazon.com/Introduction-Calculus-Analysis-Classic... [8] http://www.amazon.com/Introduction-Calculus-Analysis-Classic... [9] http://www.ams.org/journals/bull/1943-49-01/S0002-9904-1943-...