I have used Avast! for years and trust it completely. I have also used Avast! Internet Security. I'd be using it now, but I'm low on funds until next year. I highly recommend using Avast! over AVG or Avira. It runs better than both in Windows 7, and offers a much friendlier user interface.
Avast is the antivirus I use and recommend, and even has a free version that is pretty good.
Avast offers things like a Boot-Time Scan (deeper scan, which is only offered with very few antivirus programs), Software Updater (informs you of out of date software like Adobe, Flash, Java, browsers, and lets you update them), and also Browser Cleanup (scans the browsers for unwanted toolbars or addons).
Avast is the antivirus program that I love, and have been recommending to others. It has a free version available for download as well.
Different parts of this website and downloads are apparently detected as malicious, but I believe them to be false positives, since it's less than 5 out of 50 scanners detecting it (less than 10%).
As an Avast! user for many years now, I wholly trust this site and their products. They distribute free antivirus software with optional premium options that give more features. The free version is the basic version, and does not include the VPN or firewall technology that the premium versions do, but it does an incredible job at keeping viruses out and eliminating them if they happen to make it through. Great community forum, very nice customer support, great software, just an all-around great site. I highly recommend it.