Cron automatically mails anything on STDERR to the address in the MAILTO environment variable. You can set that at the top of your crontab, or else in the command line you give the crontab for your perl script. Then if things go wrong, just say, warn $msg if $condition; in your script and the news is in the mail.

To answer your question anyway, if you need to make a request to some webserver in a script, cronned or not, LWP::UserAgent is the classic choice.