Here are some great websites to practice solving for x.

Some games with different levels of skill
http://www.gamequarium.com/equations.html

Tutorials on how to solve equatios
http://www.aaamath.com/equ.htm

Allows you to choose your skills you want to practice
http://www.gamequarium.com/equations.html

Hoopshoot game - good for linear and systems of equations
http://www.crctlessons.com/equations-game.html

XP Math game - good for just getting started
http://www.xpmath.com/forums/arcade.php?do=play&gameid=69

Battleship with equations
http://www.quia.com/ba/36544.html

Practice from cool-math (may require teacher override)
http://www.coolmath.com/algebra/algebra-practice-solving.html

More practice with solving equations
http://www.quia.com/rr/4096.html

Jeopardy for solving systems of equations
http://www.quia.com/cb/79607.html

One step equation basketball game
http://www.math-play.com/One-Step-Equation-Game.html

Two step equation basketball game
http://www.math-play.com/Two-Step-Equations-Game.html