G'day Chris. I've been looking around at softboxes, umbrellas, off-camera lighting recently myself. I decided on umbrellas for their portability and flexibility. You can get some that you can use as a "shoot thru" for very soft light with a quick drop-off, or turn them around and bounce the light from inside reflector.
Not sure if you're already familiar with it, but the
Strobist blog is by far the most popular strobe/flash lighting website around. Every flash user should have it bookmarked IMO.
Lots of info and reading there, but in particular look at the drop down boxes on the right hand side. The one that says "Lighting 101", you'll see links to get you started I reckon.
Another great resource is the
POTN Flash sub-forum.