Algebra memory game:
substituting values for a variable:
 http://www.ixl.com/math/grade-5/evaluate-variable-expressions
equations in word problems:
http://www.ixl.com/math/grade-5/write-equations-to-represent-word-problems
solving equations:
http://www.ixl.com/math/grade-5/solve-equations-i
function tables: