I've never used a Garmin but I'm a big fan of my Nike+iPod.

Potential downsides:

1. It only works with an Apple iPod nano - great if you've already got one, a wee bit pricey if you don't.

2. Calibration might be an issue. I haven't calibrated mine yet and I have observed some distance error (espeically on there-and-back loops)

3. You have to buy either Nike $hoe$ with a special pocket or shell out another $30 or so for an armband + sensor pocket. (Third party)

But, if you like music while you run, already have/want to buy an iPod nano, and don't care if it's as accurate for measuring distance as a GPS unit might be, then it's definitely worth looking at.

Your options are footpod or GPS. You can google for brands and prices.

Nike+ is a cheap and cheerful footpod. You don't need Nike shoes but you do need an iPOD (not shuffle). However, they have just come out with a device to use instead of the iPOD. I had one. Works fine once calibrated. You get what you pay for and I found that it didn't like getting wet a lot...

Polar and others (inc Nike) sell running watches (w/ HR monitors) that use footpods. These have more functions yet still need calibration but will likely last longer. I have a Polar unit. Works great.

GPS - Works well outside and doesn't need to be calibrated. Will not work inside or under heavy tree cover, for obvious reasons. May take a short while to "find" satellites. Polar, Timex and Sunto offer GPS running watches but they use separate pods, unlike the Garmin, which is an all in one unit.

I picked up the Garmin 305 a couple of months ago and now I wonder what I ever did without it. I've never been in tree cover where I've lost satellite coverage and the distance measurement seems to be pretty spot on when I've compared it to the distance marks I've encountered during a race. And being able to get my per mile time during runs is an invaluable training tool. I was actually able to pick it up online for under $200 including shipping. And no, my last name is not Garmin.