World Reference has a verb conjugator: http://www.wordreference.com/conj/ESverbs.asp?v=ser plus a multilingual dictionary that you might find useful.

Check this one: http://cvc.cervantes.es/ensenanza/default.htm kisses!

I have a superb one for bending verbs. Maybe you heard of it: www.verbix.com What about this site? Check out "Language Resources" there are links there for grammar as well as other good stuff:) Buenas suerte!