Certain newer models of GPS units have a lot of fitness features including HR monitor capabilities....including the Oregon and Dakotas which we use. Which are also on clearance at Cabelas right now....
I use Polar HR on myself, and my trainers use them extensively with their clients. I highly recommend them for motivation, structure, and to track fitness gains. Simple ol' Polar for me, but the nicer models with cal counting are good, too. NO CLUE about GPS
Not for training...really not practical for every day training. GPS is too heavy and too hard on batteries for the hundreds of hours of use every year. But works great for tracking or rucks and hiking.
Timex Ironman has worked well for a few years. Use the target HR zones and audio alarms for the high and low ends. Stay in your HR zones and you will get more out of your workout.
When I started getting serious I bought a polar and I was all about it BUT I have recently set it aside... I had lost touch of what it was like to run just for the pure pleasure and challenging of running. I run as hard and as fast as ever but know I have a smile on my face instead of tracking my heart rate...
I'll use the heart rate monitor come July when i amp up my cardio training, otherwise i set it aside as Jamaro noted. I like to enjoy my time afield without the gadget and i know when i have gone anaerobic when that heart is a pounding, whether it is from the vert gain or seeing the tines!