I'm doing precalculus now, and I've found ALEKS to be interesting and useful. For you in particular it might be useful because it tries to assess where you're up to and fill in the gaps.

I also like the Art of Problem Solving books. They're really thorough, and if you want to be very sure you have no gaps then they're definitely worth a look. Their Intermediate Algebra book, by the way, covers a lot of material normally reserved for Precalculus. The website has some assessments you can take to see what you're ready for or what's too low-level for you.