This is a free site done in partnership with The University of Waterloo. At this time, it offers Precalculus and Calculus 12. With time, other mathematics courses will be offered as well. The lessons include videos, quizzes, exercises, answers, solutions, and enrichment problems. The courses are prepared very professionally with an excellent choice of problems, however some sections are still under the development. Other educational resources can be found here.
Algebra2go is a free collection of Prealgebraand Beginning Algebra related study materials designed to address the affective dimensions of student learning. Aside of very good quality videos lectures, there are class notes, worksheets, practice problems, and practice quizzes available for each lesson. The Beginning Algebra course is mostly completed but it is still under the development. There is a plan to expand the existing collection of study materials to cover Calculus as well.
This is a mostly-free site that offers about 50 videos in Arithmetic, Basic Geometry, and Prealgebra. Aside of the exceptional quality conceptual videos that are free of charge and available via the Math Antics YouTube channel, the site also offers videos with examples, exercises, and worksheets with answer keys, for a small fee of $20 per year. The entire production is done with the aid of the "Motion" software. The content, layout, animations, and timing is well thought trough before each recording. The use of graphics, colour, animations, sound effects, and occasional humor of the lecturer make those videos a real pleasure to watch. The site plans to expand to cover more topics; however, since the production of one video of such quality takes at least a month, we need to be patient before we see some coverage of algebra topics.