I have a Kryptonite braided steel coiled lock. I run it through the rear triangle+the rear wheel, the front wheel, and the saddle. I take off the saddle+seatpost from the frame and lock it up.

I was riding the light rail here in Denver, and I saw a bike locked to a bike rack, but all that was there was the fork, the cranks (and I'm assuming the bb was there), and the frame. I guess the poor soul only locked up the frame...