I just use a combination ulock from kryptonite:
http://www.amazon.com/Kryptonite-Kry...bination+ulock

It's not onerously heavy, you can set the combination to anything - I just set all my combination locks to the same combination so I never forget what it is, another trick if you're not worried about people you know is to set it to the last 4 digits of you phone number.

Cables are way to easy to cut quickly and easily with the right tools, so I never use them except for my "never let it out of my sight" high end road bike. Like I'll bike to a restaurant and get a table where I can see my bike and lock it up with the cable - if the area is a good area as well.

There are also folding metal locks - they're not light, but they're an easier shape to carry than a ulock. Security is better than a cable, but worse than a ulock:
Amazon.com : OnGuard K9 Folding Lock : Chain Bike Locks : Sports & Outdoors