I have a Garmin Edge 500. After uploading the data from a ride to Garmin Connect, I download the TCX data file and import that into a program called DashWare, which overlays your ride data onto your ride videos. I have it set to display speed, heart rate, altitude, percent grade, and distance while the video plays. Here's an example from a steep climb.

http://www.youtube.com/watch?v=R_NanMq4-xw

Here's a descent.

http://www.youtube.com/watch?v=vkdeSSTY0QE