I started learning as an adult about 1.5 years ago.
This guy does a decent series (though he's fairly annoying):
http://www.youtube.com/user/LypurThis woman has posted an enormous number of pieces played in slow motion, perfect for learning how to finger a new piece:
http://www.youtube.com/user/bbdhrgglI used the "Learn and Master Piano" video series which is fairly good if you can find a cheap or borrowable copy. Though, by the time you're done, you'll be nowhere near mastery.
I thought "How to Play Piano Despite Years of Lessons" provided a pretty good background on theory, though it gets fairly complicated fairly quickly.
Free book on piano practice methods:
http://www.pianofundamentals.com/bookDo you have a piano yet? If not, I'd strongly suggest a digital piano (with fully weighted keys) over an acoustic piano.
I think you'll find it advantageous to take occasional lessons, even if only once a month. While the resources are there for you to do it for free, playing piano is difficult and takes a lot of tedious practice. It's easy to summon a burst of enthusiasm for a few months, but having a third party monitor your progress and compel you forward is pretty crucial. If you're a huge self-starter, you may be able to muster commitment for the duration, but I find that to be the exception rather than the rule. It's going to take a minimum of 2-3 years before you get comfortable and fluent and the board (though you'll be playing nice pieces much earlier than that). It's all too easy to get distracted by other priorities and drop it.