I like using Webroot Anti-virus with Spy Sweeper. It's renowned for getting rid of everything, including viruses, spyware, trojans, worms, and adware. I've had it since 2006, and it keeps my computer perfectly clean of bad stuff, runs light on system resources (but then again I have a 3.6 GHz quad core...), and I love how few popups there are, especially when gaming. I feel safe with it, and it's won over 50 awards through the years for anti-spyware/anti-virus protection. 
For $30 you can protect one PC for a year, but I always go for the multi-user one for $10 more so I can protect as many computers as I want (usually my desktop, laptop, and parent's desktop).
I'm not trying to put down other free programs, it's just that I found this one that does the work of 2+ protection programs.