Shpider.  Copyright 2009-2010 John Morrice.

Shpider is a web automation library for Haskell.   It allows you to quickly write crawlers, and for simple cases ( like following links ) even without reading the page source.
    
It has useful features such as turning relative links from a page into absolute links, options to authorize transactions only on a given domain, and the option to only download html documents.

It also provides a nice syntax for filling out forms.

An example:

runShpider $ do
   download "http://apage.com/"
   theForm : _ <- getFormsByAction "http://anotherpage.com/"
   sendForm $ fillOutForm theForm $ pairs $ do
   "occupation" =: "unemployed Haskell programmer"
   "location" =: "mother's house"