I wear them on my Sunday AM long runs here in N. Mississippi--summer and winter--when I know the sun is going to be angling into my eyes on the return leg. I use a fairly cheap but still great looking pair from Wal-Mart. They've got a nice selection of so-called "sport sunglasses" or whatever they call them. The Jeremy Wariner look.
On the outward leg, with the sun at my back--actually, still finding its way into the sky, since I start around 6:30--I don't need them, so I just push them back on the top of my head. On the return leg, they are really nice to have.
Trouble is, if it's a humid morning, they've gotten sweated up during that first hour, and so I'll somtimes hold them in a free hand for the first few hundred yards and let them air-dry a little.
They've really been a boon, or a blessing, on days when the sun has found me--in those final miles. I couldn't care less about whether they look cool. They're just a useful training aid. They cut way down on the need to squint.
Don't spend more than $20, though. That's absolutely unneeded. Go Wal-Mart.