In my opinion there's no better practice than playing Typing of the Dead. If losing in a game irks you even a little you'll definitely improve your typing speed by playing if your current speed is slow.
I wish there was a modern sequel so deeply!
http://store.steampowered.com/app/3450/ https://www.youtube.com/watch?v=4Hr6drzeFgs
Maybe there's some artists/developers here that would want to collaborate to reduce the time burden a bit? :P
Nowadays I load the game up once every few months and I tend to beat X-Treme first shot every time, unless I get unlucky with the toxic sharks. It seems you need around 110-120wpm and decent reaction times to finish it.
I ended up switching to Speedtype on Emacs, which I've found to be far more useful, and very easy to add exercise and drills.
I don't think it's sold anywhere anymore; you should be able to find it on some abandonware website, with a bit of googling.
The menus are in japanese but the text to type is all either in english or at least uses english characters. If you want the proper english version you could try with wine, the tests on winehq seem to report decent compatibility.