MSN Encarta Article on the Celts
National Geographic's Multimedia
Presentation on the Celtic Realm
BBC Online Welsh Language
Programs
English Heritage Interactive Map
of Stonehenge and Surroundings
English Heritage Interactive Map
of Old Sarum
BBC Animation to Reconstructing
Iron Age Roundhouses
English Heritage Timeline of the
Stonehenge and Surroundings
BBC Ages of Treasure Timeline
and Game
BBC Archaeology Game Called
Hunt the Ancestor
BBC Animation of Iron Age Burial at
Wetwang and Reconstruction of
Chariot Found There
Where you thinking more in terms of courses? (please
note, I have found these online, but have not tried them all
out.  I cannot vouch for them personally)

The Gaelic College of Arts and Crafts has programs in
several locations:
http://www.gaeliccollege.edu/index.html

This is a link to the Department of Welsh at the
University of Wales, Lampeter.  They offer online
courses and it looks like some online Masters:
http://welsh.lamp.ac.uk/Department/English/about/index.php

Online Non Credit Course on Celtic Music from the
University of Wisconsin:
http://www.dcs.wisc.edu/LSA/online/celtic.htm