I got myself a Garmin Forerunner 305 a few weeks ago and I think that I'm in love. The Forerunner 305 is billed as a multisport unit. I ordered it to prepare for the half marathon that I signed up for thinking that if I'm going to run a 13.1 mile course it would kind of be handy to know how far I am running in my training. Right away fellow runners suggested that I get SportTracks. I downloaded it and got a few of the recommended plugins and I was all set.
Although I originally bought the Forerunner for running, I quickly decided that I could carry on my love affair with the Garmin by using it on my bike. Most of my cycling friends have the Garmin Edge 705 which looks really neat and can give turn by turn directions.
I managed to get about every add on for the Forerunner. The cadence sensor allows me to use the Forerunner when my bike is on the trainer and the foot pod allows me to use the Forerunner on the treadmill. Both will allow the Forerunner to function if GPS signal is lost. When I asked Garmin technical support about the foot pod, they replied, "If the watch loses the GPS connection, the foot pod will then record the distance and speed if you should have it paired up." I have read that this is also the case for the cadence sensor.
For more information, you might want to take a look at CoolRunning. There's a nice discussion of the 305 vs the 405 there.