Has an ftp site that contains various linux distributions and applications. Contains useful documents and many links to linux related resources on the net. The official site of the RedHat distribution. RedHat users must see this site. The site has huge amounts of information and faq.
Users can post questions and get the answers.
Frequently updated, and contains various kernel and other patches. This is the official site of the debian distribution. This is the linux version of the famous tucows archive. It has a nice search engine that helps you find what you're looking for. Tons of software categorized for easy access.