Scribd is a community for uploading and sharing documents that has enabled CC licensing.
SlideShare is a community for sharing presentations, documents, and PDFs under CC licenses. Various professionals are linked through sub-communities via LinkedIn, Facebook, and Twitter.
The Internet Archive is a digital library of internet sites and other cultural artifacts in digital form, including audio, moving images, texts, and archived web pages. See the Case Study for more information.
WordPress is a blogging platform and self-hosted blogging tool. In addition to easily setting a default CC license for your blog, WordPress widgets and plugins exist to make CC licensing easier.
Blogger is Google's blogging platform. Using the HTML that is generated when you choose a license, you can easily publish your blog under a CC license.