AVG 7.5
AdAware
SpyBot S&D
Zone Alarm
All free, all as good or better than ones you have to pay for. No infections, probes, or loss of information using these the past few years.
Zone Alarm is a software firewall. I use it even though I have a router and DSL modem. Both of which serve as a hardware firewall as well as their most obvious usage.
I've been using Zone Alarm for years. Works great. Kinda in my "Holy Trinity" of must use software.
ZoneAlarm - firewall
AVG - AntiVirus
Adaware - spyware