I'm a PhD student in CS and I have a fair amount of background in mathematics. But it's been many years since I studied Mathematics in college. I would like to refresh and in many cases, understand the topics more intuitively, so that I could make pictures of the equations in my head when I see them. I already read suggestions including the Princeton Companion to Mathematics, but I think I'm looking for something different. I read many papers that include some mathematical material and when I do not understand something very clearly, I would like to go back and study that topic for some hours (or a couple of days). Do you know of some book/website/material like this?
Examples of things I liked in the past are some material in betterexplained.com, this piece on matrix (Understanding matrices intuitively), and this AMS feature on SVD (We Recommend a Singular Value Decomposition).
Edit: fair amount of background in Mathematics means: someone who does not need to start from the very basic, or need resources that are without formulas and numbers; has the amount of background a typical graduate student in a scientific field like Computer Science has, but not as much as someone in Theoretical CS has.
You might try looking at "Concrete Mathematics" by Graham, Knuth, and Patashnik. The aim of the book is to give a survey of some of the topics relevant to CS (in a concrete manner and in a form useful to practitioners). Just a thought.