I just stick my Edge 305 in my back pocket or in a (webbed) pocket on my Camelbak. Seems to work just fine. I just use it mainly to track my route so I can upload it to Plus 3. More money goes to my charity that way.
I don't really use the Edge as a cycling computer, I have my trusty Ciclosport for that on my road bikes.
And on my mountain bike (did she say mountain bike?!
) I don't even use a cycling computer 'cuz I don't give two hoots about how fast or how far I go. 
You could probably pick up an Edge 205 or 305 for really cheap nowadays.
2009 Lynskey R230 Houseblend - Brooks Team Pro
2007 Rivendell Bleriot - Rivet Pearl