These sites have a collection of activities on all subjects.

Whyville

http://b.whyville.net/smmk/persPage/index

Interactive site with many fun and educational activities on various topics. Chat room is available with security measures in place.
 

Flocabulary

http://www.flocabulary.com/

Videos and songs to help you learn many topics.
 

Kentucky Learning Games
http://www.learninggamesforkids.com/us_state_games/kentucky/
This website has games for learning about Kentucky as well as many other subjects.

Utah Education Network
http://www.uen.org/3-6interactives/index.shtml
All subjects and grades. Brain teasers.

 Professor Garfield's KB Kids
http://www.professorgarfield.org/pgf_kbkids.html
You’ll find dozens and dozens of stimulating and engaging lessons that include videos and games that meet national standards and are grade specific. There are activities for grades K-6 in the subjects of math, language arts, science, and social studies.