Some links with information about programming languages that are useful when programming the kernel. Please add your links in alphabetical order.
Assembler
[http://www.jegerlehner.ch/intel/ Intel Assembler 80x86 CodeTable] an overview of the x86 assembler instructions, on one sheet of paper!
[http://www.linuxassembly.org/ Linuxassembly.org] information on assembly programming under UNIX-like operating systems.
C
Other links
[http://www.mindprod.com/unmain.html How To Write Unmaintainable Code] is a collection of excellent rules for writing code that nobody else can understand. It is an excellent article on how NOT to write programs.