If I could make my bike feel like it was going to 200mph, I wouldn't change a thing.
I've spent about 1000 miles with each option; windshield / no windshield
I can say that I definately prefer riding long distances with the shield.
There are several good bike stores out there to help you. You want a universal shield that suits your fancy. Just about any style will work with the classic cruiser shield giving the most overall coverage.
www.mawonline.com (try here first. They are usually cheaper)
www.denniskirk.com
www.bikebandit.com
www.jcwhitney.com
www.ebay.com (buy from a person. The ebay "businesses" are getting ridiculous with their shipping)
www.ronayers.com