Another great book -
The Ultimate Ride, by Chris Carmichael (Lance's coach)

Carmichael has gotten away from the heart rate zones and instead uses a recommended heart rate based on a % of your average heart rate in a fitness test for different types of workouts.
The fitness test is a 3 mile time trial, (i think he recommends doing the test twice) ... using your average heart rate during this effort gives you a much better view of your sustainable heart rate rather than a max that might only be maintained for a few seconds during the effort.
A friend of mine has a CompuTrainer that i used to do the fitness test a couple weeks ago, which will also measure watts, but the fitness test itself is do-able with your bike, a 3 mile stretch of road, and your heart rate moniter.
good luck, and happy training!