I've been using SiteAdvisor for a couple of weeks now, and I like it. From their press release:
SiteAdvisor is a consumer software company dedicated to protecting Internet users from Web-based security threats and nuisances including spyware, adware, spam, viruses, browser-based attacks, phishing, online fraud and identity theft. At the core of SiteAdvisor's ratings is a growing database of test results from millions of automated Web site visits, download installations and e-mail registrations. Headquartered in Boston with an additional office in New York City, SiteAdvisor began operations in April 2005.They say they've covered the sites that account for most web traffic. So far I've seen nothing to indicate otherwise or that they are anything other than aboveboard.
The service is free for personal use. Check it out.