JEDict is worth a look. It's free, although if you want more dictionaries it's worth buying it. And the programmer deserves support I think.
http://www.jedict.com/
It has a verb conjugation feature but only as a full sampling of the various model verbs. You can't plug in the verb you want to be conjugated. Maybe because it's relatively easy in Japanese compared to European languages.
Mind you, because Japanese is so regular it shouldn't be too hard to program this. I'm sure I've seen a web implementation somewhere. If only I could remember where...
a bit of googling later...
http://homepage3.nifty.com/jgrammar/gra ... /index.htm