Khana Academcy (or however it's spelled) is very nice. Five minute youtube refreshers on pretty much everything, so it's nice. I personally use Wolfram MathWorld, but only because I like it's comprehensive yet concise nature--which might be a little too comprehensive for what you're doing (in the sense the second half of any given article is pretty much non-applicable). Still, it's worth mentioning, since it *can* be a very useful source.
Other than that, be prepared that this is not a class that sinks in quickly, and really, it wasn't until I took calculus I understood where precalculus (my rough analog to your class) was headed. Chiefly, going in, be familiar with logarithms/exponents, power/roots, and at least a geometric grasp over trig identities (trig is the least importance since most of it will be learned in this class). That's probably the best thing you can do to prepare, since aside from new concepts, that's more or less the heart of the course: learning the ins and outs of functions using algebra.