"Commonsense Punting - A Mathematical Approach" by Roger Dedman...a good read with some really good thoughts about odds and some tactics for things like quadrellas...
"Theory of gambling and statistical logic"
"Horse racing theory and practise"
"How to make money in one day at the track"
"Money Secrets at the track"

I also have three others but i can't think of their names right now so will get back to you

Chuck