The Symbian Developer Network (at http://developer.symbian.com/) provides downloads, technical papers, system documentation as well as more interactive elements such as newsletters and discussion forums.
Tools and SDKs - Developer tools, utility libraries and API extensions, example applications, and open source projects
Library - Symbian OS documentation and technical papers.
Learning - A collection of learning resources (Symbian Press, FAQs, training)
Symbian Academy - Accredited Symbian developer programme, Symbian OS C++ Learning Paths, Symbian OS university support etc.
Symbian Signed - Symbian Signed is an industry-backed program that allows you to certify your Symbian OS applications so that they can be installed and used on S60 3rd Edition and UIQ 3 phones. Certifying an application via Symbian Signed can greatly improve the application's route and time to market.
Forums - Discussion groups and feedback areas.