Symantec for my general anti-virus software
Windows Defender to lock down system files
SpyBot SD for spyware and anything that would come from the internet
The nice thing about Defender is that it is free from Microsoft, it now comes included with Vista and 7 but wasn't around when XP first started.
SpyBot SD is also free and does an amazing job at finding and removing spyware and protecting you online.
Symantec is pretty basic and straight forward anti-virus software, I think you have to pay for it but I got it through school so I couldn't tell you how much it costs.