There are hundreds of bike locks on the market. Only a few are rated "gold" or "silver" after testing by "Sold Secure". Fewer get top marks after testing by the editors of "Cycling Plus".
"Silver" rated locks sell for as little as $30 and "gold" rated locks sell for as little as $50. It is silly to lock up a $700 bike with a "bargain" lock that has not been certified by independent testing.
In the May 2007 issue of "Cycling Plus", the editors say their tests of the Kryptonite Fahgettaboudit u-lock indicate it is the toughest u-lock they have ever seen. Totally unbreakable using manual tools. If a Fahgettaboudit is combined with the "Sheldon Brown" method, your rear wheel and frame are as safe as they can possibly be.
The editors of "Cycling Plus" invest more time and resources in their annual lock tests than anyone else in the cycling community. Folks can support their efforts by buying a copy of the May "Cycling Plus", sold at bookstores such as Borders Books, Barnes & Noble, and larger magazine stores. The $8 USA price is a bargain for the quantity and quality of information in each issue.
The correct way to lock a bike is with a compact u-lock around the rear wheel, just behind the seat tube, connecting the wheel to a beefy steel pole that is set in concrete. Do NOT put the lock around any part of the frame, as that encourages crooks to attempt to use your frame as a lever to break the lock, destroying the frame. A light u-lock, or good cable lock can be used to connect the front wheel to the frame. I replace the quick release on the front wheel with a bolt-on skewer, for extra protection.
Don't use the "standard" design "front wheel over the bar" college campus racks. Most are so flimsy that the locking rails can be pulled out with your hand. The side frame poles are stronger, but often are held on with one or two easy to remove bolts. And, those "standard" school racks don't allow use of the "Sheldon Brown" locking method.
www.soldsecure.com/Leisure.htm