I have a Garmin 500 and a Quarq. I track data over time using the free traininpeaks.com website. I use Golden Cheetah for power analysis. For real time data, I have my screens set like this:

Screen 1: 3s power, lap power, lap time. This is for intervals. I try to make the 3s and lap power numbers equal my target wattage for the interval. It's a trick I learned about here on BF from the exiled umd.

Screen 2: Speed, total time, total distance. This is pretty generic riding around data and it's what I usually look at when I'm on a group ride or on one of my Quarq-less bikes.

Screen 3: HR, cadence, kj, time of day, and average speed. This is the kitchen sink screen. Sometimes when I'm up at the lake, I'll also add elevation or elevation gain just for fun.