I used to run with a Suunto T3 heart-rate monitor, then purchased a Nike Sportwatch GPS to also be able to determine my running pace. After running with two wrist-watch devices for about a year(!) I was happy to discover that there was a heart-rate belt which could work with Sportwatch. This gave me a relatively low-cost alternative (as opposed to purchasing a new HRM+GPS device).
The pairing of the chest-strap with the Sportwatch was trivial (as attested by others, so I'll not get into details here). Once done, syncing with the chest-strap happens 'immediately' and I always have to wait a little longer for the GPS to sync.
Personally, I've configured my Sportwatch to show the heart-rate as the main display, and have pace (min/km) as secondary smaller-text above this. The large numbers are easily visible. The Sportwatch's tap-to-illuminate feature makes the display light up brightly, even for trail-running in the dark Scandinavian autumn evenings.
Uploaded stats on the nikeplus.com website also now displays heart-rate, in addition to pace and elevation which it used to do prior to my pairing a HRM. Nice to be able to see the strong correlation between heart-rate, elevation (and inversely, pace :-)
There's also a heart-rate tab on the website which displays heart-rate only for the run duration, and amount of time between to specified rates, i.e., within a zone.
Having had earlier experience with my Suunto T3 from before, personally, I feel that the Suunto is a more 'serious' heart-rate monitor with more focus on zones, training-effect, etc. For people intending to pursue a more heart-rate focused exercise regime, this would probably be a better way to go.
However, for my simpler requirement of being able to see both pace and heart-rate during my runs, this definitely fulfills my requirements, and I would definitely recommend it for anyone with similar expectations.