Reputation, malware, and referrals analysis

www.siteworthtraffic.com - analyses website traffic (users, page views) and estimates how much revenue it could generate through ads.
www.alexa.com - analyses website traffic and competitors, shows what they are doing better and gives advice on SEO improvement.
www.similarweb.com - analytics tool which provides deep information on website or mobile ranking, performance, the source of traffic, and more. On top of that, it does referral analysis.
https://sitecheck.sucuri.net - scans websites for known malware, blacklisting status, website errors, and out-of-date software.
www.quttera.com - offers free malware scanning and provides a comprehensive report that includes malicious files, suspicious files, blacklisted status, and more.
www.urlvoid.com - helps you detect potentially malicious websites. Also, it gives more information about the domain (IP address, DNS records, etc.) and cross-references it against known blacklists.