I have a Kryptonite New York Fahgettaboudit ulock that I strap to my rear rack when I think I'm going to need to lock up my bike. It's a bit longer and not quite as wide as the blue no-name ulock my daughter picked up at the hardware store for $20. I can lock the Kryptonite around the frame and through a wheel of my Specialized Sirrus to secure it to a New York City Bike Rack or random iron fence but it does take a bit of fudgetting to get it closed.

I bought mine at Bicycle Habitat about three years ago - not long after the infamous Bic pen scandal- for something like $90. If you become a member of Transportation Alternatives they give you a coupon that allows you to mail order one for about $30 less than the retail price.