I know there are some GPS units that will allow you to record each of your laps, set waypoints and be able to compare those laps with each other. So, who's used what? And what would you recommend? I have a Treo 650, is there anything that I can use with it, or will I need a dedicated unit and download to my PC?

I have a Nuvi 660, but I don't think I can do this with it, can I?

 

I own a G2X and have used the Performance Box. Both do what you are looking for, the G2X has more belles and whistles. Both have software that is not intuitive. If I was to do ti again purely for the track data I'd get a Performance Box.

 

I use a lap imer on my motorcycle when I ride trackdays.

I have an older model (6 years old) but it works great. You setup a beacon along the track that sends an infrared signal to a receiver on my bike. Automatically trips it as you go by, recording the lap times and display them.

http://www.aimsports.com/products/tg/index.html

I think this would work better than a GPS as far as accuracy with lap times.