Using Firewalls to Block Spyware?

MartinMotor asks: "I'm a Network Administrator for a company with approximately 200 users, and we just installed a shiny new PIX. Being the resourceful network geek type, I immediately started adding deny statements to kill off access to places where people can download evil cursed programs like HOTBAR. Is there anywhere out there where people like me are maintaining a list of IPs for spammers, spyware progs, and pop-uppers to add to our firewalls? I can't be the first person to have this idea."