A software keylogger is a program that can record each stroke on the keyboard that the user makes, most often without their knowledge. The software has to be downloaded manually on the victim's computer. It will automatically start capturing keystrokes as soon as the computer is turned on and remain undetected in the background. The software can be programmed to send you a summary of all the keystrokes via email.
CNET has Free Keylogger, which as the title suggests, is free. If this isn't what you're looking for, you can search for other free keyloggers or pay for one.
These work the same way as the software keylogger, except that a USB drive with the software needs to be connected to the victim's computer. The USB drive will save a summary of the keystrokes, so it's as simple as plugging it to your own computer and extracting the data. You can look through Keelog for prices, but it's bit higher than buying the software since you have the buy the USB drive with the program already on it.
