Solve Systems
http://www.quia.com/rr/59310.html
http://www.quia.com/cb/79607.html
http://www.coolmath.com/algebra/12-2x2-systems-of-equations/
http://www.crctlessons.com/systems-of-equations-game.html
http://www.superteachertools.com/jeopardy/usergames/Jan201003/game1263916458.php
http://www.coolmath.com/crunchers/algebra-problems-systems-equations-2x2.htm
http://algebralab.org/lessons/lesson.aspx?file=Algebra_LinearEqSystems.xml
(scrolldown for problems)
http://www.algebra-class.com/solving-systems-using-substitution.html
http://www.castleton.edu/math/finite/system_of_equations_practice_pro.htm
(word problems challenge site)
Video Substitutionhttp://www.onlinemathlearning.com/solving-systems-of-equations-3.html