I've got the Adidas elevation sunglasses and they're brilliant. Most sunglasses companies will only do prescription lenses up to +/- 4. Adidas were able to deal with my -10 prescription. I know I can't see beyond the end of my nose...........http://www.gosportsspex.co.uk/AdidasElevationClimaCool.asp
the glasses were about £120 (incl dark and orange lens) + £28 for the insert for the prescription lenses and then another £150 (ouch!) for the lenses. The optician I used was great and experience has shown most are pretty rubbish at dealing with sunglasses and my prescription
Only real downside at my level of short-sightedness is I lose some peripheral vision but you soon compensate so I use these quite happily biking, skiing etc.
I'll second the Elevations. Best thing is the prescription is a seperate clip in so on the occasions you do want to wear contacts you an simply clip the prescription out. Also you can change the main non prescription lenses from clear, orange right through to glacier rated lenses. There's a foam clip-on surround and arms can be replaced with an elastic strap to turn them into light goggles
My prescription was half the price of Bishopsfinger's and I bought from the same place, but then my lenses are nowhere near -10 and I got them about 2 1/2 years ago.
Very pricey but solves all problems that would niggle at me with other glasses. Worth the cost.