Yesterday HipWriterMama had an excellent post on plotting. Lots of people commented on how they plot, how they build structure, or how they do neither.
I try to plot around a basic Hero's Journey structure. To me, the most important parts of this plot structure are the Doorways of no return: two points (or however many you want) during the novel when the protagonist (hero) is put into some sort of conflict, and can no longer turn back.
And because Beth asked yesterday, I've posted my plot structure to my website here.