The Open Source Digital Forensics site is a reference for the use of open source software in digital investigations (a.k.a. digital forensics, computer forensics, incident response).
Free and open-source software is good for you and for the world. This is the best Windows software that we know of. No adware, no spyware, just good software.
Exploit Prevention Labs | Keep Your Surfing Safe: Protection from Drive-by Downloads and Zero-Day Threats - similar to McAfee's Site Advisor. Best of all, its free.