Where can I find the newest demos available for PS3? I would rather check them out from my PC.
You can find them on the PlayStation website listed under Games and doing some filtering on demos.
The problem is, these are for the US. Your profile shows Poland (might try http://pl.playstation.com/ps3/games/ to see if you can find Demos listed there), so I assume there may be some differences in what is available for your region. The other problem is, this link will likely end up changing at some point and time, so this isn't a real helpful answer and/or question.