It's not free, but I have been using NoD32 for some time now. The memory and resource footprint is miniscule compared to Norton and MacAfee. It is consistently rated among the best in AV tests. Version 2.7 is available now, but they are working on 3.0 (it is a RC that I am beta-testing now). They are also about to offer a Security Suite (who doesn't nowadays?) that is in beta test. It has a similar tiny footprint, and gives excellent AV, very good firewall, and decent anti-spam (I have yet to find an anti-spam I really like).

You can check it out at:
Antivirus Software - Eliminate Spyware and Adware with NOD32 Antivirus from ESET

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Fredrick T. Greco
Senior Pastor, Christ Church PCA (Katy, TX)
Christ Church Blog

"The heart is the main thing in true religion...It is the hinge and turning-point in the condition of man's soul. If the heart is alive to God and quickened by the Spirit, the man is a living Christian. If the heart is dead and has not the Spirit, the man is dead before God." (J.C. Ryle)