A simple keylogger written in python. It is primarily designed for backup purposes, but can be used as a stealth keylogger, too. It does not raise any trust issues, since it is a set of [relatively] short python scripts that you can easily examine.
Strokey is a small hardware keyboard logger saving all keystrokes into an EEPROM memory for later investigation. The device may get attached to any PS/2-keyboard by intercepting the cable, or get placed directly inside for maximum invisibility.