You'll find
this useful. Look under number 2 (for AntiVirus), 3 (for AntiSpyware) and 17 (for advanced spam filters). You'll also find firewalls, browser protection and others on that page. Be sure to check out link 4 under AV utils for good discussion of free vs pay AV solutions. Also, there's no reason why you can't have more than one of each type of security software installed; just be sure only one of each kind is actively protecting, and set a schedule for the passive ones.