http://www.gfi.com/blog/top-20-free-disk-tools-for-sysadmins/

(short introduction below; go to original link for all the goodies )

Here are 20 of the best free tools that will help you conduct a digital forensic investigation. Whether it’s for an internal human resources case, an investigation into unauthorized access to a server, or if you just want to learn a new skill, these suites and utilities will help you conduct memory forensic analysis, hard drive forensic analysis, forensic image exploration, forensic imaging and mobile forensics. As such, they all provide the ability to bring back in-depth information about what’s “under the hood” of a system.

This is by no means an extensive list and may not cover everything you need for your investigation. You might also need additional utilities such a file viewers, hash generators, and text editors – checkout 101 Free Admin Tools for some of these. My articles on Top 10 Free Troubleshooting Tools for SysAdmins, Top 20 Free Network Monitoring and Analysis Tools for Sys Admins and Top 20 Free File Management Tools for Sys Admins might also come in handy since they contain a bunch of tools that can be used for Digital Forensic Investigations (e.g. BackTrack and the SysInternals Suite or the NirSoft Suite of tools).

Even if you may have heard of some of these tools before, I’m confident that you’ll find a gem or two amongst this list.