I have just installed SiteAdvisor by McAfee and am finding it useful, thus far. It provides ratings for websites which are safe and unsafe. By unsafe, this can mean a variety of things from spyware, pop-up ads, and online scams. I was afraid it would slow down my web surfing experience, but this has not happened, thus far.
SiteAdvisor can be downloaded free of charge at http://www.siteadvisor.com
Tech Spinning 