I think it depends, in part, on where the scope of your responsibilities lie and what kinds of tools are already in use on your system and in what languages they are written. The rationale for this is that if you have to go beyond scripting administration tasks to debugging administration tools, you'll want to be familar with whatever language those are written in. For example, a lot of the system configuration tools on a Fedora/Redhat system are coded in Python, so knowing that might help debug those tools if you encounter a problem. On the other hand, if you're maintaining a Horde/IMP installation (or other PHP-based web interfaces), then knowing PHP will come in handy.

I wouldn't get too caught up in what language are "cool" -- I'd focus on what other languages are in use around you every day.