http://www.timwerx.net/language/jpverbs/index.htm
I found this to be very helpful. It's romaji only, which bites, but his book has the kana, which is good.
I like the base 1-2-3-4-5 way it teaches and how it coincides with the Japanese order of vowels a-i-u-e-o (well, for yodan verbs anyways). Most sites are like 'take the pre-masu form of a verb and add tai.' Well, 'pre-masu form of a verb' doesnt register very well with me. Instead, I prefer hearing base 2, because i is the 2nd letter of the alphabet and thus goes with base 2, so I can think "Ah, i. So its asobitai."
However it doesnt mention some of the more casual, slangy forms of verbs. For example, for 'to have to do something' is only given as -nakereba narimasen. However, Ive also heard -nakucha, -nakya dame, and -nakya ikenai. It doesnt mention those.
