I use bar end mirrors on my bikes.
Zefal make several models; the Cyclop is wide angle and somewhat distorted, although it doesn't require finicky placement. The Spin is quite small, but most versatile for mounting on both flat bars or drops. The Dooback is larger and I like it on my commuter bike.
Mirrors - ZEFAL
In the past I have also used the Louis Garneau mirror ($11.99 Cdn), but it will eventually loosen up and cannot be totally tightened.
https://garneau.com/int/en/cycling/r...r/black-020-60
I have just ordered this "Motorcycle" mirror from eBay and am anxiously waiting to try it. Hopefully will be more robust than the above mentioned cycling mirrors, although it does not fold away.
Lastly I tried this palm mirror with Fat Bike, for winter riding - requires some hand movement but overall works quite well.
http://static.dudeiwantthat.com/img/...rror-20037.jpg