php would be useful if/when you're doign anything web-based (php & perl work well in tandem)...knowing C/C++ is always
a good thing for a perl programmer (perl, among others, is written in C, so any perl problems are inherently C problems). so php and mabye
C (depending on your future projects) would be my suggestions for you
though you can do just about anything in perl, sometimes perl isnt the best
way. for instance, if you're aiming for fast, small, standalone executables, C would be the way to go. if you're looking for cross-platform with minimal porting, Java. it's not always "you can do that in perl", sometimes its "you can do that more efficiently in ******* language".
Give a man a match and he'll be warm for an hour. Set him on fire and he'll be warm for the rest of his life.