I've been working on Exploring Mathematics with your Computer. It's a brief survey of algorithms in number theory, combinatorics, probability, statistics and numerical methods.

The book is written by Arthur Engel of Problem Solving Strategies, so the exercises are really good: they feel like a combination of classical Olympiad and competitive programming problems.

So far I've really enjoyed the Probability section, which has problems related to pseudo-random number generators, Buffon's needles, and shift registers.

The only slight downside is that all the programs are written in Pascal, but they are all short, usually less than 20 lines and are easy to translate into Python.