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Broadly speaking I think that you are speaking about two things: derivatives pricing (this is what people think when thy talk about quantitative finance) and algorithmic trading (which can be either pure market making or alpha seeking speculation ;)."Quantitative finance" was mostly associated with derivatives pricing in the mid-late aughts, but nowadays I see a pretty loose classification tossed around that essentially makes it shorthand for "we're doing something data science-y to forecast things." It's more of a marketing/cultural term, and has sort of lost a lot of the meaning and precision it used to have. Handy to sort of succinctly sum up where on the Street you vaguely work (or at least which ingroup you'd like to signal therein), but not so handy for trying to e.g. Google around for what to learn. QuantStart is probably helpful there though.
Not a criticism of your point, just wanted to add some color to it for other readers. I agree with Wilmott forums being a great starting point at the very least, though it's going to be a little esoteric for someone totally new to finance.
To the OP: pick up Heard on the Street: Quantitative Questions From Wall Street Job Interviews. It's not perfect, but it's a good start. There aren't any textbooks that will take you all of the way in algorithmic trading (from finding alpha, to strategy implementation, to risk management, to portfolio theory, etc). If you're a CS student and looking for quantitative finance, core computer science (not just programming) is what you want to drill down on. You'll want to invest in your math skills quite a bit too, and especially statistics.
Research firms like Two Sigma, RenTec (good luck), AQR, D.E. Shaw and Bridgewater, which are wholly or in part devoted to what you might call "financial engineering." Learn about their processes and talk to as many people in the industry as you can to learn about what they do and network.
Finally, chollida1 does this better than I can, but please don't trade with your own money. It's an expensive tuition :)