Typingweb.com is how I went from about 50 words / minute pecking to 80 touch typing. After you get to a certain point with the tutorial the only thing that you can do to get faster is practice. One of the world class typists used to type out a 1000 word block of text each day, starting over whenever he made mistake (this was after he retired.) If you don't have any writing assignments that you are obligated to do, I suggest copying a few pages worth of articles each day. Alternate focusing on perfect accuracy for one article and then focus on speed for the next. Eventually you should get faster.

While I don't remember how difficult it got, I know I loved Typing of the Dead. Orbs the old "House of the Dead" game, but users a keyboard instead of a light gun! Of course, good luck finding a legit copy...

Very impressed with Z-Type: http://www.phoboslab.org/ztype/

If you already have a good foundation and just need to practice, typeracer is excellent.

http://play.typeracer.com

play.typeracer.com

try out gtypist if you use Ubuntu.