Danny's comment about heart rate monitors reminded me to mention something I've been waiting for since earlier this year: the Garmin Forerunner 405.
Before I talk about the Garmin, however, I want to note that my Polar F6 has worked great for the last year and it's given me no reason to replace it. It has settable heart rate zones, keeps a history of my workouts, and works well overall as a heart rate monitor. The only small complaints I've had are that the watch is a little too easy to switch into workout mode while in my gym bag; and, the instructions don't clearly note to dry off your chest band when you're done with it1.
But...the new Garmin does all the same things as my Polar and it's got a GPS in it for tracking where I'm exercising. That's really hot. It's also three times as expensive, but whatever.
I won't go deep into details—the Garmin blog has some posts and a video. It's got a lot of totally kickass training features, and I'm excited to pick one up when it comes out in April. April!
1 This is really important for preserving the battery in the chest strap. Leaving it with a little bit of sweat (or other moisture) on the contacts will keep the transponder running for hours longer than it needs to.
At least Garmin is saying more about the 405 release date. I've been wanting to get Bonnie one of those for at least three months now.
"Specialty stores around April 21" is the best I've been able to extract so far.
Pricing appears to be varied, so definitely hunt around before buying.