One of the coolest uses for perl that I've been playing with a lot lately is for interpreting esoteric languages. I've tried writing interpreters in c and gave up pretty soon.

For a personal project, I constructed a new esoteric language called Obfuna, the interpreter for it that I wrote in perl was great. Small code, fast, and easy.
I also wrote an interpreter for another language, condit which although seemingly less obscure in its syntax turned out to be a bitch to parse.

I won't post the code here as it's far too long. Maybe it'll make it into craft one day when I've cleaned it up and commented properly.