The Dragon Naturally Speaking Preferred is a low cost voice recognition software that I use. The less typing I do, the better. I started using Dragon at version 6 and have found that it has improved substantially. It includes a good quality headset that can be replaced with an even better one, once you have found the software useful.
The speed and accuracy is pretty good and I like the voice web navigation it offers. Dragon does require some training time but the results speak for themselves. It is not perfect but less typing = more healing. It is hard to use in an open office environment though.
Windows 7 has rudimentary voice recognition software built in. Give it a try to see if you like it, then upgrade to Dragon if you are serious.
iPhones and iPads have Siri voice recognition. While it does not learn from errors, it does help reduce typing.
Keep in mind that this software is very sensitive to noise in the room, so you cannot play a radio, have the heater running, or have it function well if your computer is very loud.
A high quality headset microphone is important for achieving maximum accuracy. This website has some reviews of different microphones. I use the Parrot VXI headset with an Andrea USB soundcard for maximum voice recognition performance.