Why zip-tie free? Zip-ties are some of the easiest to replace items on the planet. And can be bought just about anywhere, and there are only a few sizes. O-rings can and do degrade over time-and you have to hunt for the right size.
Garmin Edge 605. It only uses GPS, so there are no sensors to attach to the bike. You will, however, use zip ties to attach the computer mount to your bars or stem. The downside is that you can't use a cadence sensor or heart rate monitor. If you don't care about that info, then the 605 is a good choice. Mine has been trouble-free for two years. (knocking on wood now...)
Several new Trek and Gary Fishers have location built into right fork for sensor, they call it Speed Trap. Could be pricey alternative if you don't already own one though http://bontrager.com/model/07058
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