There are several services that allow SSHing via AJAX. That is, instead of using firewall-piercing techniques that many other solutions suggest (which can get you fired), these send everything over 100% standard HTTP (or HTTPS).

Unlike firewall-piercing methods, these are incapable of TCP port forwarding, and thus, are considered by corporate security people to be far more safe in comparison.

pretty thorough Wikipedia page

Services

ones that I've used for long chunks of time (for some reason, most end up not working from work at one point or another)
- anyterm (my.anyterm.org) ($$) [periodically fails at 2010-Oct]
- GoToSSH.com ($$) [periodically fails at 2010-Oct]
- consoleFISH ($$) [work blocked this 2012-02]
ones that worked for me so far
- SSHTerm (free)
- WebSSH.cz.cc (slooow) [work blocked this 2010-Oct]
ones that seem to be permanently broken for some reason or another
- webssh.homelinux.net (free) [website completely down]

Software

Software that would let you run your own service.

GateOne