Argh! How could I write about web filters without mentioning two of my favorite filters:

• The Eater of Meaning. It turns any web page into brain-bending mush. See for yourself. It even eats HTML comments! I've saved two copies of it's output because it's just so cool. And it's written in Python and you can download the source.
  
  
• The bizarre search-and-replace CGI tool by 'yoz'. See what it can do. Hack the URL to create your own effects. I have already used this for practical jokes - few people check if the URL they click on is the URL the browser is displaying...