This book helped me massively:http://www.amazon.co.uk/Maths-Chemistry ... 0199541299
The Sigma (big E) was explained very simply as is capital Pi.
I like the comparision of the For loop to explain Sigma, as this is how I see it. The Pi is not summing, you multiply instead.
This book is excellent too, I have it electronically and paperback: http://www1.maths.leeds.ac.uk/~khouston/httlam.html
It explains some quite ubiquitous symbols like R, Z, N, Q very early on (Real, Integer, Natural, Rational numbers) then goes into Set notation - just as a topic used to illustrate the thinking about part. I've a lot of these books as I really, really need to get higher maths to do the more interesting jobs out there.
I've a lot of other books on thinking mathamatically, including a delightful volume known as The mathematical mechanic that teaches proving in a visual way.
The cognitive aspect of maths, for me, is about how I represent it to myself. Until I learned enough code to get into trouble, I couldn't "get" simultaneous equations - now that I get the simple notion of variables I can do simple versions of such in my head. The same goes for differentiation - which to be fair is just a rule anyway, something programmers are good at. It's just how its represented. The dense symbols used, really do fox me a lot but gradually some of it is beginning to clear. The set theory symbols are worth knowing cold - if you look up List comprehensions on wikipedia, there's an explanation shorthanded into symbol form that actually makes plenty of elegant sense the moment you get it.
Anyway, I'm on a ramble and on a similar journey to yourself!