Try www.proxify.com (no so well known so will probably not be blocked)

Works very well on chat boards. I advise suscribing as they limit bandwidth otherwise.

All done via HTTPS so its pretty secure from remote line monitoring in most cases.

They give you many ways of access so if they block the site name or IP address there are hundreds of other ways in !

However, if your network has VNC (or equivilant) installed, they can still capture your screen image so be carefull...