In perusing the NaNoWriMo forums, I came across a term about outlining a book I hadn't heard before - the Snowflake method. One Google search later, I found the method here.
As luck would have it, it closely approximates what I've done so far with my novel. I've got a fifteen page outline, which I got using a combo of character sheets from First Draft in 30 Days by Karen Weisner, a six-act screenplay structure I got through my online class at Write Tight Now, while incorporating elements of Joseph Campbell's Hero's Journey. I'm supposed to move on and do an extensive outline now, that approximates a first draft. But I may just start that first draft for NaNo. Anyway, the Snowflake method looks cool, so check it out if you're inclined to outline but don't know how.
Also found free mindmapping software called Freemind that looks like fun to use. I downloaded it and without any instruction just started making a mindmap for a different book idea I've had for awhile. I'm not sure if this will be useful for outlining so much as a way to generate ideas and get the creative juices flowing. It's probably also useful for less creative types who need to brainstorm for their business or research or something. No idea what mind mapping is? Check out Wikipedia's definition here.