I use a single Garmin Edge 500 now for my three bikes. I just pop it on to the one I am using for the day and it has setting for each bike so it knows which one I am on, and if there are extra sensors and such I have configured, wheel size, etc.

But before that I had a CatEye Velo 9 that did everything I wanted from a basic, wired, cycling computer. It is cheap and works well. Battery life was great. I only had it on one bike though, of course. The bike I used most. Coupled with a cycling phone app in your pocket or saddlebag will then have your realtime speed/distance/time and the phone also records your GPS data for later analysis on sites like Strava if you care for that stuff.