Prominent examples of digital libraries include Project Gutenberg, which offers free access to thousands of public domain e-books, and the Internet Archive, which preserves websites, books, audio recordings, and videos. Google Books, while not a traditional library, has digitized millions of books, making snippets or full texts available online. Digital libraries face unique challenges, including copyright issues, digital preservation, and ensuring equitable access. However, they play a crucial role in democratizing knowledge and supporting global research and education efforts.