A favorite among many, most students can relate this to a popular television show.ABCYA
This is one that all grade levels use. The higher the grade level the more choices of activities there are. Students are welcome to go above their grade level.Starfall
This site is neat for all levels, but my 2 youngest grades enjoy it the most. Great for both reading and math development.Edmodo
A great collaborative site to use in class as well as home. My upper grade students join the group created by me and have access to many things.