Garmin has recently releasded the Garmin 10.
It is a smaller unit than the 205 (it's predecessor), and comes in more color choices as well. It also has a smaller price tag than the 305.
If you do not plan on training or racing with heart rate and just want distance and pace, this is the watch for you (if you want to buy something new).
https://buy.garmin.com/shop/shop.do?cID=142&pID=107143
http://www.runningwarehouse.com/descpage-GMFR10S.html
Now, if you don't mind buying used (which every Garmin I have ever bought has always been used), eBay can offer some good deasl on used and refurbished 305 and 310 models.
The biggest difference between the 10 and the 305 is heart rate and personal customization (like racing against a virtual partner, calories burned, etc.). The 310 is built more for triathletes so you can swim in it and has a longer battery (18 hours) for Ironman compeition.