i have gone through many proxy servers that worked, but they all were eventually blocked at my school.
here are a couple that worked for youtube, and thus have a good chance at working on other sites:
http://www.youtubesupreme.com
http://www.unblockyoutube.biz
http://www.kproxy.com (not sure if it will work, but give it a a shot)
here are a couple that didn't work for youtube:
http://2access.info
http://secure88.info
proxydude
April 2009