These are links to sites found either by me or former students which have been useful:

2 Unknown Calculator
Use for checking your answer to a system of equations.
http://www.1728.com/unknwn2.htm

Adding Fractions with Different Denominators
From AAA Math, this site nicely explains how to determine the LCD. It also has a problem generator.
http://www.aaamath.com/fra66k-addfracud.html

AlgeBasics
Watch free algebra tutorials about algebra.
http://www.algebasics.com/

Division
Nice explanation which visually identifies the divisor, dividend, quotient and remainder.
http://www.mathsteacher.com.au/year7/ch01_whole/05_div/div.htm

Equations and Inequalities
Work with Unit One at this time, so you don't get confused.
http://www.veazeys.com/math/lessons.htm

Exponents
Covers the basic exponent rules, explaining how to remember them and use them.
http://www.purplemath.com/modules/exponent.htm

Factoring Polynomials
Further explanation of factoring.
http://www.factoring-polynomials.com/

Factoring x2 + bx + c
Interactive site which helps you understand how to factor trinomials.
http://karensworld.com/algebra/algebra2-1.html

Factoring - Practice
From the Oswego City School District Regent Exam Prep set
http://www.regentsprep.org/Regents/math/factor/pracfact4.htm

Irrational Numbers
Makes learning math fun.
http://www.mathisfun.com/irrational-numbers.html

Least Common Multiples
Use this site to not only learn more about LCMs, but also how to work with fractions.
http://www.helpwithfractions.com/least-common-multiple.html

One Mathematical Cat
http://www.onemathematicalcat.org/algebra_book/online_problems/table_of_contents.htm
Algebra topics, well-presented, with interactive exercises. From Dr. Carol J.V. Fisher, Monterey, MA.

Polynomials
Explains the definition of a polynomial with examples.
http://www.purplemath.com/modules/polydefs.htm

Polynomials
Interactive graphs help individuals explore polynomials of degrees up to 5.
http://www.analyzemath.com/polynomial2/polynomial2.htm

Prime Factorization
This is a simpler way to determine PF.
http://www.gomath.com/algebra/factor.php

Prime Factorization Machine
This site should be used to CHECK YOUR ANSWER. Don't rely on it to solve your problem.
http://britton.disted.camosun.bc.ca/jbprimefactor.htm

Properties of Real Numbers
For Associative, Commutative and Distributive properties.
http://www.math.com/school/subject2/lessons/S2U2L1GL.html

Pythagorean Theorem
This explains section 4.12.
http://www.grc.nasa.gov/WWW/K-12/airplane/pythag.html

Quadratic Equations
Solving quadratic equations and solving by factoring.
http://www.purplemath.com/modules/solvquad.htm

Scientific Notation Exercise
http://science.widener.edu/svb/tutorial/scinot.html
Use to practice scientific notation

Subtracting Fractions with Different Denominators
From AAA Math, this site also helps you determine the LCD, before completing the subtraction. A problem generator is included.
http://www.aaamath.com/fra66l-subfracud.html

System of Equations - Calculator
http://www.analyzemath.com/Calculators/Calculator_syst_eq.html
Two online calculators and solvers for systems of 2 by 2 and 3 by 3 linear equations.

Systems of Equations - Solving Systems of Equations Algebraically
http://www.regentsprep.org/Regents/Math/syslin/AlgSysAdd.htm
Using addition or subtraction.

Systems of Equations - Solving
http://www.purplemath.com/modules/systlin1.htm
Solving by graphing, substitution, elimination/addition, and Gaussian elimination. From PurpleMath.

Using Equations to Solve Percent Problems
Additional help. http://www.themathlab.com/Algebra/algebra%20lessons/section3proportions/a370equations%20to%20solve%20percent%20problems.htm

Word Problems: Percent of Increase and Decrease
Further clarification for these types of problems.
http://www.algebralab.org/Word/Word.aspx?file=Algebra_PercentsII.xml

Word Problems
Basic math problems - some easy to solve, some hard.
http://www.algebrahelp.com/lessons/wordproblems/basics