I have had for a couple of years a pair of yellow polarised shades, and found them to be excellent when fishing in smaller rivers where rtree cover brings shade. They are also first rate driving glasses, especially in fog.
I have just bought on ebay a pair of polarised sunglasses with a small magnifying 'bifocal' bit at the bottom, only £15, and saves using cocoons or flip-downs. Link:
eBay My World - eye-special-eyes
A final observation - I started my fly fishing on a local river, and had been catching fish, until I changed sunglasses. Didn't twig the problem until I caught my reflection in the water - mirror shades flash back at fish. Caught nothing with them on, started catching again when they were replaced.
dan