My networking husband's knowledge and his 4 expensive, hardware firewalls that stand between all our pc's and the ISP router. That and common sense, constant back-ups, not randomly surfing the internet much and rarely downloading anything. In 15 years I've had one ad-virus (where ads keep popping up until it crashes your pc) that necessitated a re-install and that's it. If you back up a lot, it's not that painful to reformat/reinstall.
Since I use Windows7 now I let it do the anti-virus scanning on certain downloads, but that's all I have. I've tried some of the $100/free stuff in the past and they're all terrible (imo) for one reason or another, but certainly a lot better than nothing if you feel you need it.
- Java disabled in my default browser
Yeah, I do that a lot too.