I can't recommend any sites as I learnt this where I worked. It's a great scripting language though, i'm sure you'll enjoy using it.
Why are you bothering? if it's for web based stuff, don't bother - PHP has usurped it's position. CGI is as dead as a dodo. That said, it's still very nice for in the *nix shell. More power than BASH. Buy "Learning Perl" by Mr. Schwartz. Can't go wrong with O'Reilly books.