This is an interactive site discussing matrix operations:

http://www.mathportal.org/calculators/matrices-calculators/matrix-operations-calculator.php

This is an interactive site finding inverse matrices:

http://www.mathportal.org/calculators/matrices-calculators/matrix-calculator.php

This is a nice matrix operation site which also includes Gauss-Jordan elimination:

http://matrix.reshish.com/inverse.php