Protecting Content

My company provides various reports and dynamic website content to clients whose websites we design and host as well as to clients who have their sites designed and hosted elsewhere. We do not want people to be able to easily link to our content or bring it up in an iframe or whatever unless they are a paid subscriber. We would like to be able to limit the content to the domains of paying clients and keep it from displaying elsewhere. Note also that out of several reports, publications and content we offer, clients can mix and match, subscribe to just one element or all of them (The subscription levels are managed by us on the back end.)

Currently we have a system that is built in Perl/Postgres SQL and it is problematic(constantly failing and not very secure) Also it requires that the content be loaded into an iframe on the client's site or linked directly. We would like a solution that is PHP-based and can talk to our existing database. We would also like to be able to display the content on the page without an iframe so it is more search engine friendly, etc.

An off-the-shelf solution would be preferable if one is available - and we like to support the open source community.