typingtest.com: It is one of the best online apps that help to improve your typing speed. It measures your speed and accuracy in recreating the text given.
typingweb.com: Typing Web is a free online typing tutor for typists that offers you some entertaining typing games and typing tests also.
rapidtyping.com: It is another great app that has an attractive interface which can encourage you to improve your typing skill. This apps explains the concepts and gives some tips to improve your typing speed.
play.typeracer.com: Type Racer is the first multiplayer typing game on the web that allows people to race each-other by typing quotes from books, movies, and songs.