Oakleys are expensive, and the £5 ones are not up to the job - perfect middle ground would appear to be these www.golf-sunglasses.co.uk
great quality, price and versatility - and the lens specs are designed for golf. The green lens is great, and the light enhancer awesome.
I have the prescription pair, so I can't claim to be an expert on the others.
Has anyone else tried them? Not sure about the idea of the ladies' pair (my missus says she doesn't like the colour!), but the other non-prescription glasses look decent.