Well there are the usual suggestions (textbooks, subject-based help books like X for Dummies, Khan Academy, etc) but I've been reviewing using Screencast videos posted by my College Algebra/Trig professor. The Math 147 videos represent an entire semester of PreCalculus classes; 1 50~ minute video per day, 5 days a week for 16~ weeks.
I think the best way to do it is to watch each exam review (an overview of the topics covered on the coming exam) and see if you know everything. If you don't, go back and watch the video on that topic and move onto the next exam review. There are a lot of videos (naturally) and they're in different formats so that people can watch them no matter what system they're on.. so that is a little annoying.
If you sort by Name, at the top you'll see '08Exam1Review - Flash'. At the bottom you'll see 'PCExam2Review - Flash', 'PCExam3Review - Flash', etc. Like I said earlier if you run into something on the Review that you don't remember, check out a video like.. welll, say you didn't remember symmetry on Exam1Review you could watch '04PC2.4 - Flash'. I don't know how long they'll be up, as she has several courses to teach this summer and it's possible she'll delete them -- but the Spring course has been moved to a Summer folder so hopefully that means she's not deleting them (yet).
If you're interested the first review is at: http://www.screencast.com/users/mjroletto/folders/Math%20147%20Summer%202012%20Videos/media/be718add-b2bf-40d7-8a51-1e7153816901
The PreCalculus playlist:
http://www.screencast.com/users/mjroletto/folders/Math%20147%20Summer%202012%20Videos
Her library:
http://www.screencast.com/users/mjroletto
You can find College Algebra and Trigonometry playlists there as well, but everything in those courses + some stuff specific to PreCalc.
You won't have access to the PDF files, reviews, etc that enrolled students are.. but this should give you an idea of what you don't know. You can pause the video and work through the problem before she does.. that's what I do anyway. Hope it helps.