I just picked up a used Casio Keyboard (LK-90 TV) with the hopes of teaching myself piano and expanding my knowledge of music theory. I do, however, need some good advice as to what on-line resources, applications, and/or programs are best-suited to help me. Good books too!

I started playing guitar about 4 years ago as a hobby. I took lessons from a friend with a strong background in piano who picked up the guitar as a teenager and took lessons from a jazz player. Besides teaching me how to play some songs, he also dropped a heaping of theory on me as well: terminology, circle of fifths, chord sets, scales, modes, etc. Unfortunately, I haven't been able to keep up with regular lessons, so I don't grasp the theory and I don't have someone keeping me focused. Maybe I haven't found the right teacher--but something just hasn't clicked, and I'm not making the connections on my own.

That said, I decided to give the guitar a break and get acquainted with the piano, in hopes that by applying the theory to it I'll be able to understand the music better. I've always been told that learning piano is pretty much the launching pad for every other instrument anyway.

If you have any suggestions or advice I'm all ears. Thanks for reading this.
Pianos are keyboards, but keyboards are not pianos.
Call me Batman.
Semantics aside, if you're just beginning, I'd grab just a basic reference text "Piano for Dummies/for idiots/whatever", and learn the basics of the instrument. That is: Scales, chords, intervals, etc...

Find a bunch of piano music you dig and grab some sheet music. Get a teacher, if you can.