I've used WWW::Mechanize more than anything, and it works nicely for a lot of scripting of browsers, LWP::UserAgent does it too, and I've used Selenium previously, which can be very useful if you need to figure out how to get at the part of the website you want and it's too painful to pick through the forms and HTML code.

"Spidering Hacks" from O'Reilly has a lot of good information about various perl tools, and "Perl & LWP", also from O'Reilly also is good. There's also a good amount of information to be had on the net about these tools, although I've found the two books I've mentioned to be the most useful sources for me, at least given my novitiate state.

Good luck.