I use the mirrycle MTB mirror on my hybrid drop bar bike. I just put it in the bar end and adjust it so I can see behind me - the mirror in this position doesn't actually add any width to the bike. It is very useful to see what is behind me - not so much in the rain though! Pretty stable, and nice and cheap.

I also have the STI mirrycle on my road bike - haven't tried it out yet though.

If you want I can post a pic of my current setup.

Daven