Martin,
Your best bet is to buy a Polar. Nike, Timex, etc. all have their own offerings, but Polar has always been the innovator in the space. They have a great website, too, that will recommend several models to you based on likely usage.
www.polar.fi
You'll want one with high and low alarms to keep you in the proper HR range on long endurance workouts. Aside from that, there are many bells and whistles that are nice to have (interval timers, download capability, compass, altimeter, etc ad nauseam) that can push the price over $300, but if you wait until after Christmas you should be able to get a good basic model for under $100.
Buy Sleamaker's book and you'll learn more than you ever wanted to know about HR ranges for specific workout types (and seasons). Try to find someone that can hook you up with a maximum heart rate test - I typically found that I could get someone in the cardio lab at the local hospital to do one for free after hours just for novelty value. Don't try to do one on your own just by jumping on the treadmill and going - there's a good chance you'll gray out at the end and you need someone spotting you.
It's important to have as a baseline, though, as the popular formulas for estimating MHR can be way off. The most frequently cited is to subtract your age from 220, but some years back that would have suggested mine was about 200. I got my HR up to 219 on the treadmill, so using 200 as my max would have meant I was doing all of my workouts way to easy.