Here are some great websites to practice solving for x.

Some games with different levels of skill

Tutorials on how to solve equatios

Allows you to choose your skills you want to practice

Hoopshoot game - good for linear and systems of equations

XP Math game - good for just getting started

Battleship with equations

Practice from cool-math (may require teacher override)

More practice with solving equations

Jeopardy for solving systems of equations

One step equation basketball game

Two step equation basketball game