Homepage by Greg Hoglund, author of Exploiting Software.
Many works done on rootkits. Mainly for Windows.
Many articles on hacking, cracking and so on. The famous article on
buffer-overflow, "Smashing the Stack for Fun and Profit", by Aleph One can
also be obtained on this site.
Undocumented Windows NT
You can read this book on the inside of Windows for free.
As the title suggests, many of the contents have never been documented
Fairly new site about rootkits, exploits and reverse engineering.
Has many useful stuff if your working deep inside the kernel of
Has a lot of exploit codes for various kind of software
vulnerabilities. (Executables, Web Apps, etc.)