I'm using a Garmin FR60, I really can't recommend because I did a lot of searching to find the one that would suit my needs, and some features, like using it underwater while swimming, I'd be a little hesitant to try (I probably wouldn't need that info if I went lap swimming anyway). Notwithstanding, I do think it's really cool.
It keeps a constant read out of HR throughout that I can check at a glance, records & graphs with desktop software so I can log & compare workouts. It does everything I need and so far has worked very well. There is a huge difference between perceived exertion and actual HR stats or there can be, let's say. The other thing I record is morning & evening HR, mostly for signs of over training and adequate recovery. Even at my level I think it's important & necessary, to reach my goals.
If you're smart phone enabled, you may want to check out this app,
ithlete....it does, or says it does a more accurate account of energy expenditure & recovery rate, I would imagine runners would find it particularly useful.
http://www.ithlete.net/
Alas, I have the Flintstone Fone, and live in a cave, so my methods suit me for now, and I'm quite happy with the results...