Introductory Mathematics

Mathplanet.com was created in spring 2011 to spread mathematical knowledge worldwide. Everything on the site is free to use for non-profit purposes and you don't need to register in order to watch videos or read examples.

Recommended for PreAlgebra through Algebra 2 and Geometry.

Paul's Online Math Notes: Cheat Sheets and Tables An excellent, well-organized site by teacher Paul Dawkins. Covers very basic to advanced math topics. 

IXL - Math for the Left and Right Brain  Site visitors can complete up to 20 questions each day to brush up on basic math. For unlimited access and use of extra features, paid membership is required.

 Geometry

 Manga High Games-based learning site where students learn mathematics via purpose-built casual games that balance fun and learning.

Trigonometry

Free Trigonometry Tutorials and Problems from AnalyzeMath.com. 

FlexBook: CK-12 Trigonometry, 2nd ed. FlexBook is a free online textbook.

Statistics

Statistics How-To: Elementary Statistics for the rest of us!  Site owned by a former math professor. 

Calculus 

The Calculus Page Problems List

Calculus I Practice Exams and Solutions by Alberto Corso at the University of Kentucky.

Differential Equations

Students Solutions Manual: Partial Differential Equations with Fourier Series and Boundary Value Problems

Solutions Manual to Introduction to Differential Equations with Dynamical Systems

 Colleges and Universities

The Mother Lode of Online Practice Exams.  More than a hundred links to practice exams in math at all levels at other colleges and universities.  (You're welcome.)

Massachusetts Institute of Technology Open Courseware -- you can educate yourself for free by taking MIT's Open Courseware classes. Materials are the same as those studied by tuition-paying students.

University of Houston online Math help Click on the class link that corresponds to your level. Online text is available, homework assignments and odd-numbered answers, some video support. 

Practice math at your own pace with Khan Academy's exercises. You can start at 1+1 and work your way into calculus or jump right into whatever topic needs some brushing up. 

Each problem is randomly generated, so you never run out of practice material. If you need a hint, every single problem can be broken down, step-by-step, with one click. 

The iOS app lets you download videos to your device and watch them offline at your own pace. It also lets you track your progress to get credit for watching videos, and see your achievements. 

XtraMath provides rewarding supplemental math activities and makes them available for free. Students complete practice activities that are recorded and shared with teachers and parents. Teachers can create classroom accounts in which each child has his or her own log-in credentials. Parents can also be given log-in credentials to see how their children are progressing.

California Free Digital Textbooks Initiative Download pdf textbooks for high school-level geometry, trigonometry, statistics, and calculus. Sponsored by the CK-12 Foundation.  Browse all CK-12 textbook offerings here.

500 Free Online Courses from Top Universities

Get free online courses from the world’s leading universities. This collection includes over 500 free courses in the liberal arts and sciences. Download these audio & video courses straight to your computer or mp3 player. Math courses are found here.