The linked problem sets can be found here (the links on the 6250 site are behind a wall). Also, when not specified, the text links are to Moon & Stirling's
Mathematical Methods and Algorithms for Signal Processing.
How to Solve It, Polya, 1945. Classic introduction to mathematical problem solving. (Amazon)
Introduction to Probability, Bertsekas and Tsitsiklis, 2008. Good introduction to elementary probability theory. (Amazon)
An Introduction to Probability Theory and its Applications, Feller, 1950. An absolute classic. A more advanced (but still accessible) introduction to probability theory. (Amazon)
The Art of Probability, Hamming, 1994. Another introduction to probability theory written by a fellow engineer. (Amazon)
All of Statistics, Wasserman, 2004. Exactly what the title says. (Amazon)
Linear Algebra and Its Applications, Strang, 2005. A great introduction to linear algebra. (Amazon)
Convex Optimization, Boyd, 2004. We will cover the tools from convex optimization that we need as part of the course, but if you want to know more, this is a great resource targeted towards electrical engineers. (Free online version, Amazon)