FlexMath is a free online basic course in algebra.  It is designed for use in conjunction with classroom instruction, and it guides you through 9 units and 84 lessons up to quadratic equations.  It’s a flexible alternative for students with heavy sports schedules, who are ill for extended periods of time, and for homeschoolers with parent instructors.  Teachers and students can track their progress, and teachers can create a calendar with assignments and due dates.

cK-12 has several free online digital algebra and pre-algebra textbooks for students and teachers in grades 6-12.  There are editions for students and teachers, and textbooks that include the use of graphing calculators for Algebra 1 and 2.  You can read the textbooks online or download them.

There are also accompanying study guides for algebra topics.

ChiliMath offers math lessons targeting various topics covered in a regular algebra class such as multi-step equations, slope of a straight line, factoring, etc.  The teaching approach is to discuss the concepts along with concrete examples, and diagrams for visual learners. 

Emphasis of this site is on comprehensive textbook-like, step-by-step explanations. Practice problems are in worksheet format.

From site:  This interactive mathematics resource allows the user to explore the order of operations (brackets, exponents, multiplication, division, addition and subtraction). The resource also includes print activities, solutions, learning strategies, and a math game.

Free Math Help Algebra provides textbook-style lessons, flash videos showing how to solve a huge variety of algebra problems, a list of the most commonly used formulas, and a forum where you can get answers to vexing problems.