I've been wanting to do this for a while now here's my top 3 free antivirus programs.

1.Avira Free Antivirus

Download -  http://www.avira.com/en/index

Pros:
- Completely Free
- Light
- Fast
- Includes Anti-Spyware
- High Detection Rate
- Low Amount of False Dettections
- Regular Updates

Cons:
- No Firewall


2.AVG Free Antivirus

Pros:
- Completely Free
- Good Scanning Speed
- Includes Anti-Spyware
- Low Amount of False Dettections
- Regular Updates

Cons:
- Not as light as the other two
- No Firewall


3.Avast Free Antivirus

Download - http://www.avast.com/en-eu/index

Pros:
- Completely Free
- Fast
- Includes Anti-Spyware
- High Detection Rate
- Regular Updates

Cons:
- No Firewall
- A Significant Number Of False Dettection