Disc locks work nice - but lots of people tend to forget them.... A long neck padlock could fit over just about any brake rotor. A regular chain or cable and padlock would also work. I've seen front brake lever lock, that holds the front brake and the cable then attaches to like a bike rack, or sign post. What it comes down to, is that it's just a deterrent. How intense are the thieves in your area? any system can be beaten. Tell us how safe you want the bike and we can probably find what you're looking for.
Edit: The best security of all is insurance against theft...