I did plenty of mavis beacon and such and hated it (though it drilled the basics into me, at least) and used the DOS command line a bit, but what made me fast and accurate was busy real-time chatrooms and IM. Basically Yahoo Chat and ICQ, especially the former. If you wanted to chime in you had to be very quick. If I'd never found something that forced me to be fast if I wanted to participate, I might well still be a crappy, slowish typist.
Online games were also great for this! You have to type quickly so that you can keep up with actually playing the game, and you can't stare at the keyboard because you need to keep an eye on what's actually going.
