I'm convinced that for 90 percent of the people out thereeven those who are serious enough about training to watch their heart rate to ensure they don't over or under traina monitor with the bare minimum of functions is fine. And no, it doesn't have to be Polar, although that brand makes excellent monitors. An exceedingly good bargain monitor, in fact, is the Polar A1just $50. It has current heart rate, average rate, and time exercised. For the same price, Performance Axiom's HR-150 adds full watch functions, plus programmable target= levels and memory recall of time spent in the target=ed zone. Peformance's electronics are all pretty good, so I should think that would be a reliable buy.
If you want to go with a luxe monitor, Polar's S210 ($175) is a great oneit has a wide range of options for setting and recording maximum heart rate, shows calories burned, has full watch functions, and is water-resistant. A great monitor.