There is a Prolog course (at Birmingham University) available
over the web at
http://www.cs.bham.ac.uk/~pjh/prolog_course/se207.html
This site also has information about other public domain Prologs.
Amzi!'s site provides several Prolog learning aids:
http://www.amzi.com/products/learning_products.htm
There is also a guide to Prolog programming at
http://kti.ms.mff.cuni.cz/~bartak/prolog/index.html
Finally, the WWW Virtual Logic Programming Library contains links to all kinds of logic programming resources:
http://archive.comlab.ox.ac.uk/logic-prog.html