In reply to mypyrex:
I got a pair of sunglasses from these folk in 2003:
http://www.optilabs.com/
Mine are called airquest but i think the replacement is canyon.
And they have been fantastic.
Primarily for mountain biking i've used them for climbing, motorbikes, driving and in fact virtually any activity everytime there's a bit of sun.
Great for long days outdoors. They're tough and pretty damage resistant... providing you don't drop them on to gravel then grind them in with your foot.
The only thing you'll have problems getting from your optician is your pupil distance (i think).
I went for brown polarised lenses which are great at handling quick changes between light and dark (e.g. popping into trees on your bike). I've never had a problem with them steaming up and they work well into the gloaming so you won't be fumbling for your normal glasses until it's almost dark.
If you're going to use them with a bike/motorbike helmet i'd recomend thin legs so they fit easier over/under/in to straps or pads.
i could go on but i won't. buy them, they're great.