Cisco firewall/PIX to block a website

in summary, use websense.

PIXes are not layer7 devices, it sits on L3/L4. You can block via IP addresses or ports, but if the website has many IP addresses (ie google.com or yahoo.com), then you are always adding more IPs to your ACL.

http://supportwiki.cisco.com/ViewWiki/index.php/How_to_configure_access_rules_on_a_PIX_Firewall_to_block_streaming_audio_and_video_applications