As for a basic setup, I'd say you need the following:
Wide lens (I assume we're going to talk about lenses later)
A good on-camera flash that dials down to very low power - 1/64th or lower.
Actually, you can do quite good work with just that alone- check out this photog's stuff, all done with one on-camera light:
Flickr: Photos from tlpacheco
However, it constrains you in terms of what you can shoot. The SB80's are a good choice for a remote because you don't need anything special to trigger them remotely, so that's what I'd recommend.
Strobist is really THE place to learn about off-camera stuff.