(Sample link) White House for Kids http://www.whitehouse.gov/kids/whlife/index.html
(Sample link) National Geographic for Kids http://www.nationalgeographic.com/kids/
http://www.funbrain.com
Basic Literacy (sounds, letters, etc.) http://www.starfall.com
Virtual FieldTrips http://www.midgefrazel.net/fieldtrip.html
Various Activities http://www.readwritethink.org
Preschool on Up (all subjects) http://www.bbc.co.uk/schools/
Brain Boosters http://www.school.discovery.com/schrockguide/