There is no tiered system like Xbox Live Gold and Silver. Instead, all basic online services are free.
The only place you'll be asked to fork over a penny is when you purchase something in the PlayStation Store - all of the online services, from sign-up right through to voice and video chat, are free, as is normal multiplayer gaming.
The PS3 also offers a web browser. It is a fully featured proprietary browser which allows you to visit any site on the web. Xbox Live does not have a browser and Nintendo has teamed up with Opera to offer their browser.
All in all, this is a very informative article for those of you who want to know more about the PS3 Online system.