Sandboxie
Another difficult one to explain this but basically it stops viruses from getting onto your computer rather than the traditional method of trying to find viruses and cleaning them. How does it do this? Well the way i think of it is to imaging the internet in a box, imagine your hardrive in a box. Ok well normally viruses just go straight from the internet to your computer. With sandboxie a new box is created inbetween your pc and the internet. Anything that is picked up or downloaded is now put into this new box.
You get to check what is going into the box before it is put onto your hardrive so you can stop any nasty bugs getting through. You can even download some programs, try them out and delete them without anything being added to your hard drive. Now i'm sure this all sounds terribly confusing but within a few hours of me downloading it i soon got my head around it and most importantly i haven't had a single virus since using this.
The only snag i could think of is that not everyone would be able to spot a potential threat and may accidently let a bug get through to there hard drive but this would be extremely rare and your virus protection should pick it up anyway.