http://www.amazon.com/Kryptonite-Fah.../dp/B000OZ9VLU

That said, with enough time, any lock can be broken. The best security is to not leave an expensive bike out where people can take it. The second best security is to lock it up next to a bike that looks nicer and has a crappier lock than yours, in a heavily trafficked area. Put the U around the rear wheel between the stays. That will effectively lock the frame and rear wheel (with the lock there, the rear wheel can't be removed without cutting the wheel). Then put the cable that you already have through the front wheel, rear wheel, and frame.