Thanks for the replies so far everyone. I confirmed on my last ride yesterday (a 25 mile loop I just started) that every road I ride, from backroad to highway (nice big shoulder), has powerlines.

P. B. Walker - Thanks for recommending the Timex HRM's. I'll seriously consider them, it's just too bad they don't have a bike specific model.

Both my bikes need service, so I'll find out what my LBS opinion is as well. They host Sat. morning rides, so I'm sure they know how much interference there is. If it's not too bad, I will go with one of the Polar's.