NOD32 4.0 is in it's first beta, and NOD32 are letting anyone test it completely free of charge until the release. This includes full updates for virus definitions and everything.
In my own experience, NOD32 has always been the most lightweight anti-virus on the market.
Note: I don't condone using beta software for everyday use, however, I have not had a single crash since I've been using it. Your mileage may vary.
nod32 is a fantastic product, but i dont think i would use beta anti virus software. good find tho.