html/latest - Kernel Documentation (mainline)
html/next - Kernel Documentation (linux-next)
README various README files scattered around Linux kernel source
LP64 standard defining the size of char, short, int, and long on 32-bit and 64-bit platforms. (See also the rationale for the standard, and the legacy reasons another OS declined to adopt this standard).
Linux Foundation's specs page (ELF, Dwarf, ABI...)
All Linux Weekly News kernel articles indexed by topic
Linux kernel changelog (summary of what's new in each version)
H-Online's Kernel-Log (most recent first)
Understanding the Linux Virtual Memory Manager, online book by Mel Gorman.
If you have any questions or concerns, please email helpdesk at kernel dot org.