Plugin or mod for paid membership sections?

Hello,
I am currently in the process of creating a website that will ultimately use WordPress as a CMS and integrate bbPress as a forum.

What I want is for users to be able to sign up a free account, see most content, but then there will also be the ability to upgrade your account. With an upgraded account you’d be able to post in the forums, and some pages would have content that you wouldn’t see unless you were logged into an upgraded account.

Will this need to be custom coded or is there an existing plugin or modification that could solve this?

Thanks a bunch in advance!