First of all, there's no "decent quant finance book" in existence.

But there are attempts at it. Most notable are:

- "An Introduction to the Mathematics of Financial Derivatives", by Neftci

- Wilmott books aren't bad.

- Brigo's "Interest Rate Models" is... flaky. It is a lot of material and seems to be quite rigorous, until some point most crucial for understanding, which gets skipped over. The interviews with traders at the end are good.

- Only buy Choudhry books, if you want to talk good about finance.

The gold standard for quant books: Hull's Options, Futures, and Derivatives.

http://www.amazon.com/Options-Futures-Derivatives-DerivaGem-...

This is very much a beginner's book. When I interviewed for internships in the summer of 2008, the interviewers expected that I would already be familiar with a large portion of the content of this book.

It really depends on what you're trying to achieve. The skills and knowledge necessary for long-term equity investment, short-term statistical arbitrage, derivative pricing and high-frequency trading are all quite different.

Investment Science by Luenberger