Heart Rate Monitor for Working Out at the Gym

I saw a Nike monitor at Costco - not sure on the price.

Another vote for a Polar heart rate monitor. The cardio machines themselves are simply not that reliable. I highly recommend a HRM, because not only are they accurate at telling the user their heart rate, letting them know how long it took to get in the THR zone, how long they stayed in the THR zone, how long it took for the heart to recover back to resting rate (a good indicator of overall fitness), and allows them to gauge how their level of fitness changes and improves over time. All of this data can be very motivating - you say he is 'suddenly working out all the time' and you are 'waiting for it to wear off'; a HRM will likely help motivate him to continue on this healthy lifestyle decision. A healthier body typically means a happier person - and you get to reap the benefits of a husband who feels great about himself :)

Many machines at the gym already have a heart monitor built in to monitor you while working out. Most treadmills and elipticals have them. I guess I don't see the necessity unless there is a heart or pulmonary problem. I have gotten familiar enough with what the machine reads and how my body feels to pretty well guess whether I have reach my target heart rate.
This may be a passing thing...go cheap! Maybe an inexpensive one on a wrist watch?

I work out regularly and use a Polar F1 HRM. Polar is a great reputable HRM that is reasonably priced, a snap to set up and use, and is dependable and accurate.