I'm now using BitDefender which got top marks in a recent MaximumPC paid-for AV round-up review. The BD Internet Security suite is good for 3 PCs for two years which is great. I only buy AV software when I see it on sale. I also MSE on a couple of other laptops in the house and it works good too, especially for a free one. In the past I've used Kaspersky, ESET, and Norton.
G74SX-DH71 | + 256GB Crucial M4 SSD , 16GB DDR3 SDRAM, Intel Centrino 6230 WiFi, Win 8 Pro
Peripherals: Steelseries Ikari laser mouse, Razer Ferox speakers, Audioengine D1 dac, Shure SRH840 headphones