CoolMath has a lot of example problems with explanations and a couple of practice problems for each topic.
SOS Math has a couple of examples for each of their topics as well as a few practice problems with answers. Their only Pre-Calculus topics relate to matrices, but who doesn’t need to review those?
Wolfram MathWorld covers topics from Algebra through college-level mathematics.
SparkNotes Math has notes about all levels of math, divided up by topic, complete with practice problems and solutions.