I do a lot of typing every week, probably more than most folks. But I'm certainly not the fastest in my field. To improve that there's TypingWeb, a Web-based typing tutor the likes of Mavis Beacon and other software-based typing helpers. It's been around since 2004 as a paid service, but has just opened its doors to everyone for free.
The service offers a few ways to enhance your typing, including lessons in the home keys, correct finger placement, and handy shortcuts, and bundles them with exercises that apply what you've just learned. It's not nearly as slick as some of the more recent typing efforts I've seen, like Keybr or the addictively fun TypeRacer, but the lesson plans for each difficulty level are really well thought out. You can simply pick and choose areas where you want to improve on and dig in.
To go along with these tests, the service monitors your progress to becoming a typing legend. You can view this advancement on a chart that will identify your improvements (or decline) in general accuracy, as well as raw words per minute, and that number combined with your accuracy (which may be lower).
Some of the lessons can be insanely difficult. Fulfilling just one part of one difficulty level is a veritable barrage of testing. Near the end of any section the tool simply won't let you continue to the next step until you fulfill a certain requirement either in accuracy, speed, or time.
After spending some time brushing up my skills I noticed a decent improvement on the typing test I had taken before I began the course, although the wording hadn't changed, so I think I had a leg up on it from the last time. Who knows how much better I'd be if I had the hours (yes I mean it) to go through the rest of the lessons. You could do these tests for weeks.
One thing I find amusing is that there's an iPhone app for TypingWeb for those who need a little work maneuvering Apple's somewhat cramped QWERTY touch keyboard. It doesn't go nearly as in-depth as the desktop version, but I suppose it's a good tool for people who don't send text messages or write e-mails. The test is also a little easier with your phone in landscape mode--giving you the keyboard that's about twice as wide. However, I don't think that's the point. Existing TypingWeb users will need to sign up again, but anyone can try it out anonymously too.