Join Date: Apr 2012
Location: Ontario, Canada
Bikes: Rivendell Sam Hillborne DTT in Awesome Green; Brompton M6R (reduced gearing) in Sage Green; GT Timberline Hybrid (10 years old!)
I'm wrestling with this issue as well, and wouldn't you know, no one mirror works with any of the three bikes I have - kind of frustrating. I find that most of the mirror mounts these days are intended for the flat bar style handles so prevalent on MTBs, hybrids, etc. Some other mirrors for other handle styles are just, well, ugly and ungainly.
However, one mirror that I did find relatively useful and can be easily moved from one bike to another is this one from axiom:
The rubber strap is pretty secure, and relatively easy to attach and detach. The middle bolt loosens sometimes and then the mirror dangles down: have your multi-tool handy!
The mirror is a little too super convex for my liking: a little less curvature would be just right.