For lower back, deadlifts, deadlifts, deadlifts, and finish it off with some back extensions. Oh yeah, don't forget deadlifts.
They are second only to squats for most useful exercise, in my opinion.
Twists are very much for the obliques. I warm up with my abs before working out, and get some twist crunches in then. Aside from that, I keep my twists to a bare minimum, as I like the "fingers" on my obliques, but am careful not to work them too much.