I really like the National Cycle brand "Street Shield" that came with one of my bikes many years ago. It mounts to the handlebars and upper forks, and can be removed/replaced within a couple of minutes as long as you leave the mounting hardware installed on the bike. I used to use it in the Winter when I lived in Denver, but it hasn't gotten any use the last couple of years here in Texas.
It's about 17" tall, IIRC, and is the perfect height for me at 5'7" and with Euro sport bars, because the top edge is below my line of sight, but it still directs the air over the top of my helmet, so there's no buffeting.
If you're having issues with high winds, though, a bar/fork-mounted windscreen may cause more problems than it solves. They're very nice for keeping the wind off your body and relieving windchill and fatigue issues, but in high cross-winds they act like a sail and will pull your bike all over the road.
