Typing Web

http://www.typingweb.com/

Free with registration.  Multiple levels and certificates

 

Typing Tutor online

http://www.typingtutor-online.com/EN/Aspx/SelectExerciseWithCharacters.aspx

Another free site with multi-levels

 

Sense Lang

http://www.sense-lang.org/typing/tutor/keyboarding.php

Another free site with multi-levels

 

Type Racer

http://play.typeracer.com/

You can practice typing skills or race against others online.