Web service SiteAdvisor tells you if a web site has known spyware, pop-ups or if it spams users after you register with an email address:
SiteAdvisor helps protect you from all kinds of Web-based security threats including spyware, adware, spam, viruses, browser-based attacks, phishing, online fraud and identity theft.
Our automated testers continually patrol the Web to browse sites, download files, and sign-up for things with e-mail addresses. As you search, browse, download or register online, SiteAdvisor’s safety ratings help you stay safe and in control.
A browser plugin for Internet Explorer and Firefox is available for download which alerts you realtime to sites with the cooties. Otherwise you can just pop a URL into their search box and get information about a site that way. SiteAdvisor will come in handy when you’re looking for sites notorious for hosting malware, like song lyrics or ringtone sites.