On the free end you have AVG
which are my favourites. I'm sure others have their own. BTW, don't ever run more than one at a time, more is not better in this case.
Everything that irritates us about others can lead us to an understanding of ourselves. -- Carl Jung
eVGA X58 tri-SLI, i7 930 @ 3.8GHz., Corsair 6GB Dominator, Inno3D GTX470, eVGA260
ASUS P8P67 Pro, i7 2600K @4.60 GHz, 8GB RAM, eVGA GTX 460