The green bar is displayed in the address bar on web sites which have undergone a process of Extended Validation (EV)as part of their SSL application process.

During the application process the organisation applying for the certificate has to positively prove that they are who they say they are. Documentation has to be provided to the certifying authority who will validate it's authenticity. They will also perform other checks, before issuing the certificate.

An EV certificate then shows to the web site browser that the web site is genuine and that they are who they say they are.

The certificate authority also offers a financial warranty should it laster transpire that they were not and that they failed in their validation process, often running to over a million dollars.

You might think that all certificates are the same, and while mechanically most are, however they are issued for different purposes and with differnt levels of warrantee and features and so are at different prices.

Rapid SSL for example, are all about speed of issue and is domain validated but offers a very small financial warranty regarding it's validation process, where as Geotrust, Symantec and others offer domain validated certificates with higher levels of warranty, site seals, and go futher with organisation and exended validation processes.

They also offer certificates that can be used to sign code and which can also be used for multiple subdomains or domains.

We do offer certificates that can be used for muliple subdomains or SANs - Subject Name Alternatives.

With these types of certificates you could secure noth jsut your main www.yourdomain.com address but also portal.yourdomain.com and shop.youdomain.com with the same certificate.

Some certificates include 3 to 25 subdomains as standard, and cal be expanded to include 100 or more.