Like all things, the best way to improve typing speed is to practice. And as with all forms of communication, the most effective practice is practical experience. I've found that typing tutors and typing tests can help establish muscle memory and familiarity with key placement, but the real speed improvements come from using touch typing in my daily activities - everything from email and docs to IM conversations.

Accuracy, however, is a different matter altogether. Accuracy for me improves with good spelling. I can copy things, and copy them fast. But nothing comes off my fingertips faster than a word that I can recognize quickly and spell correctly in my head. When I know how to spell the words, my fingers just have to use muscle memory to touch the right keys. Otherwise, I have to stop to read every letter.

I use the Natural 4000 keyboard. It's the most comfortable that I've ever used for typing. However, the key spacing makes gaming a little challenging when the setup is for one hand on the mouse and the other on the keyboard. But for regular typing, I really enjoy it.