Jamyang Bath Buddhist Group - follows the Tibetan tradition of Lama Tsongkhapa.
Monasteries in the Theravadin Thai Forest Sangha lineage of Ajahn Chah - contains information on the tradition, and dhamma resources. Also see:
Gaia House - retreat center.
Samatha Trust - a long established lay Theravadin group which offers meditation weekends for beginners at its retreat centre in Wales.
Zen Gateway - articles, discussion, etc.
Access to Insight - contains a wealth of Theravadin material
Talks, writings and translations of Thanissaro Bhikkhu - a teacher in the Theravadin Forest Sangha Tradition