You can develop a good estimate of your maximum heart rate here:
http://www.howtobefit.com/determine-...heart-rate.htm. There are both submaximum and maximum tests.

The other important point is your lactate threshold (50%+ anaerobic [=no oxygen use in producing energy]). This is the point where your breathing changes, and you can no longer talk (except possibly in gasps while breathing out). This is about 8 on the perceived exertion scale. This can vary from about 75% MHR in inactive, untrained people to about 80% MHR for active people to about 85% after extensive training. This is something that training can greatly improve. I found this easiest to estimate when on a spinning bike / trainer. Joe Friel bases his zones around the lactate zone, and has tests for this in his training books.

Max heart rate is different for different activities: highest for running, intermediate for cycling, lowest for swimming. This has to do with number of muscles used, especially large ones; position of body relative to heart; and amount of cooling. Cycling is tricky because just going from the bars to the hoods will change your heart rate slightly, by about 2-3 beats, without any change in exertion - your heart will beat slightly faster to pump blood upwards. (Try this indoors on a trainer or spinning machine so that air resistance and cooling doesn't come into play).

Book resources:
* Joe Friel -- complicated to follow (includes level, time available for training, goals, weaknesses, peaking for the most important events) -- but you develop a training plan that is very individualized. The training plan essentially starts in the "off-season" in the fall, and has you peak during late spring / early summer. It is essentially a year-long plan.
* Base Building for Cyclists -- by a Joe Friel student, essentially expanding on what should be done in the off-season to build up your aerobic base.
* Sarah Bernhardt -- she just came out with a book that has training plans for people from novice to intermediate for centuries, multi-day tours, and mountain biking. These are a lot shorter, typically about 2 months. I am planning to use a modified century plan in Sept-Oct to fill in the rest of the biking season, then switch to Joe Friel to develop a year-long plan starting in the late fall.
* Sally Edwards has a lot of heart training manuals, but I have not used these so I can't comment.