All under the sun ( :-)

http://www.brokenthorn.com/Resources/OSDevIndex.html
http://en.skelix.org/skelixos/

The lost Skelix OS tutorial's Mirror
(1-page mirror, IE compatible, no rar files, better than nothing)
If anybody has those rar files, please share!
http://skelixos.cyberine.com/

Daniel's Blog
http://himmele.blogspot.com/2011/07/build-your-own-operating-system.html

German Tutorial
http://www.fh-zwickau.de/doc/prmo/pmtutor/text/index.htm