Here are some of the larger sites run by Tibet support organizations, as well as good sources of information on Tibet in general.
TibetNet - Tibetan Government-in-Exile Multi-Lingual Site in Dharamsala
Tibetan Government-in-Exile site in London (www.tibet.com)
Tibetan Children's Village
International Campaign for Tibet (ICT)
International Tibet Support Network
Students for a Free Tibet
Tibetan and Himalayan Digital Library
Tibet Justice Center (formerly International Committee of Lawyers for Tibet)
Tibetan Centre for Human Rights and Democracy
Independent Tibet Network
International Tibet Independence Movement
Tibetan Community Switzerland and Liechtenstein
Tibet Initiative Deutschland e.V.
Phayul.com - News on Tibet by Tibetans
Hear Tibet! Campaign for Tibetan Self-Determination
The Committee of 100 for Tibet
Tibet Fund
Swiss-Tibetan Friendship Association
Worldbridges Tibet
Tibet Information Network (TIN)
Canada Tibet Committee
Free Tibet Campaign
Kotan Publishing "Tibetan Cultural Region Web Directory"
World Wide Web Virtual Library: Tibetan Studies
PeaceJam, with Nobel Peace Laureate His Holiness the Dalai Lama

Tibet Support Groups in Italy
All-Party Parliamentary Group For Tibet - Italy
Altrimondi Tibet
Amici del Tibet - Friends of Tibet-Italy
Associazione Italia-Tibet
Associazione Villaggio Terra
Ewam Centre, Florence
La Casa del Tibet - Italy
Gruppo Sostegno Famiglie Profughi Tibetani
Yeshe Norbu Appello per il Tibet