Ebay Sell glasses (well in the UK they do!) with the clear lenses in. Ie pre-perscription, and they don't sell for a lot of money either. I've bought about 20 pairs over the last few years (you can see some pictures of some of them, in my picture threads that are listed in my signature!)
All glasses come from the makers with clear lenses, but the lenses normally have printing on them. you can remove this by using nail varnish remover on the paint and then quickly cleaning them before the NVR has time to react with the plastic. (all of my glasses have been cleaned like this!)
I have really good eyesite, only needing (with age) glasses for reading and close work, but as Tracy I think glasses enhance the look and also add to the illusion of being fem, ie people don't expect someone to be wearing glasses unless they really need them!
Also different glasses really make a difference, the ones I'm wearing in my avitar look really good with a bob, however they look awful if I wear a strieght wig, so it really is worth having a seach and seeing if you can find some. I probably have about 30+ pairs now.