Agony & Ecstasy
Agony & Ecstasy is a free spanking site on everything about spanking (and other punishments). It has a very detailed list of spanking implements and interesting articles on the history of spanking. The site is bilingual, in English and Spanish. Selected articles have also been translated to other languages (French, Greek, Russian).
The content of the site has changed some time ago. It looks like domain owner has changed. Actual site does offer nothing interesting.
Note: I look for a contact for authors of the original site, to get an permission to re-publish original articles about bondage. The original site offered nice tutorial about knots, bindings etc. Contact me here: http://www.forumbondage.com/bforum/showthread.php?tid=1167