I like this mirror from Cateye - fits onto end of drop bars or flat bars, or even off the barends on flat bars. I find it has a nice angle of view for me, even with rear panniers, and that I can adjust it easily. It generally stays in place while riding, but will move if you hit an obstacle. I found it for about $5 (US) sold as a Cateye racing mirror:

http://www.cateye.com/en/products/vi...d=8&subCatId=0