Tim's Takamatsu Verb Lessons

This site is great. It covers both a lot of verb rules in a clear manner and a lot of vocabulary along with it. Good for beginners and for more advanced students: http://www.timwerx.net/language/jpverbs/index.htm

Detailed explanation on Japanese Verbs

Really good website for Japanese Verb Gammar: http://www.epochrypha.com/japanese/materials/verbs/

Verb Bases

http://oasis.fortunecity.com/labreya/147/verbchart.html