Sebek2 - A Kernel-based Data Capture Tool
LogError writes "Sebek is a piece of code the lives entirely in kernel space and records either some or all data accessed by users on the system. This paper is a detailed discussion of Sebek, how it works and its value."
This can just as easily be modified and used by blackhats as an advanced rootkit, though. Like everything, it's a double-edged sword.