I have a Garmin Edge 705 and an old Forerunner 301. The Forerunner series have a software package that calculates your HR zones for running only, based on changes in your HR at different speeds over several workouts that include anaerobic intervals. I've never done a true LT calculation but the Forerunner's calculations seem to match my perceived exertion pretty well. Because there are so many variables that affect cycling speed, the software only works on your running profile.

Now, I know that max cycling HR is normally 5-10 bpm lower than max running HR, but I don't know whether the zones translate from running to cycling as well. Anyway I love my gadgets, but I'm a total data geek.