The one's I would look at are the Garmin 305, 210, and 610. Depending on what you want to spend and the features.
I have the Garmin 305, and it has served me well for a couple years now. A little big, but it is light. I really do not notice it that much. It is accurate (based on races). I have worn it in pouring rain, and it still functioned perfectly.
I think the 210 is kind of like the 305 in functionality. It is based on pushing buttons. More like a sports watch, as opposed to the 305, which will really only be worn when running. The 210 has a nice price. This forum gets 15% off at runningwarehouse.com, and I know they have the 210 and 610.
The 610 has more features. It is also a touch screen, instead of relying on buttons. It has a much steeper price. So the question is whether or not it is worth it for you. Alot of the features may not be necessary, but are probably fun. I am thinking about getting it myself.
Stay away from the 400's. They have that bezzel screen, which is known for being buggy. It often doesn't work when wet (this is a problem if you sweat). I also heard it was not as accurate as the 305.
Stay away from the new Nike GPS watch. I had it and returned it. Did a terrible job with the pace. One second I am under 7:00/mile, the next second I am over 9:00/mile. My pace does not change that dramatically that fast. I heard Nike just upgraded the software to help fix this. I have not heard if they were successful though.
Just my thoughts...