Sophos Anti-virus - Protects your MAC from security attacks.
Believe it or not, for MOST users, this is sufficient protection, and the price is right!
Download it here: http://www.sophos.com/en-us/products/free-tools/sophos-antivirus-for-mac-home-edition.aspx
OnyX- Maintenance, Optimization and Personalization of your System .
Download it here: http://www.titanium.free.fr/
Handbrake - The Open Source Video Transcoder.
Download it here: https://handbrake.fr/downloads.php