Microsoft Security Essentials (free antivirus)
Windows antivirus straight from Microsoft. Back in the day, Norton was the best, but it became slower and slower, and is now one of the primary causes of computer instability and slowness. I then used free services like AVG until they started being far more pushy and annoying. I stopped using AV altogether until Microsoft came out with MSE. It's extremely lightweight, as I've never noticed it slowing my system down, and it provides as good or better virus protection than the competition as shown in independent reviews.
All virus protection is about the same. All the researchers talk to each other. The difference is in the engines and the irritation factor of using the thing.
I have often benefited from recommendations for Things I Didn't Know I Wanted.
Given that Less Wrong is a community of unusually intelligent, critical, and self-improvement-focused people, I suspect we can generate a pretty helpful thread of product recommendations — perhaps even a monthly thread of product recommendations.
Rules: