I use http://www.gmaps-pedometer.com for my routes. Now, it may or may not agree with the bike computer, but it's at least consistent and since I use it for all the routes, then I have some sort of measurement system.

You can also save your routes so you can share or refer back to them. I keep a list on my del.icio.us
http://del.icio.us/sydspinnin/Routes