I personally like Malwarebytes. I tested it along with numerous other anti-virus software, and it consistently had the highest detection rate, and is much more lightweight than McAfee (which is the worst in my opinion, I used it for a year), Norton, AVG, etc.
Sandboxie is also a good piece of software to compliment any anti-virus program, though it is not really an anti-virus program itself, it makes tracking shit down much easier,