OK... the company I work for has blocked pretty much any traffic other than port 80 out through the firewall. Is anyone familiar with any software for port forwarding or proxying chat from behind a corporate (read: untouchable) firewall?

Try this one....

http://www.meebo.com

It runs from the internet

Blocked here. I even tried the trick of going through the Babelfish site, which is blocked as a remote proxy site...

Sounds like they have the firewall pretty well locked up and it is a good bet that they are also watching the traffic that is trying to get out through the firewall so I would be carefull on what you try to do.

I agree, any company that goes to the lengths of blocking all traffic except port 80, and (I assume mail ports?) including remote proxies is likely to have a lot of monitoring in place as well.

Pop a wireless card in and see if any unsecured networks are being run in the area, if so, easy firewall bypass :)