You forgot www.securityspace.com too. This site runs nessus, and if you register, you can have a full nessus scan carried out on your IP address. Be warned though, it takes time, and can crash your PC if it's vulnerable to some of the DoS tests. I should mention though, that if you want the full details of any serious problems discovered, they'll charge you for the results. You get full details for minor problems though.