I know this subject has come up a number of times in the past...
I haven't yet tried it (being at work..
), though I plan to this weekend. This should allow you to pass IMs, Avain, Email, all past your work firewall to your home machine which redirects it to the correct server.
http://www.zunta.org/blog/archives/004498.php
From one of my fav sites (that I can't get to from work, gabnabit!):
http://www.hackaday.com/