I did not read through all the responses, so I'm sorry if any of these have been listed. I have a 6 yr old (soon to be 7), and I have been getting a lot of lesson plans, art activities and info off many sites as well. Here are some that come to mind:
Information sites:
Discovery Kids
Word Central
Scholastic
kidshealth.org
Smithsonian.com
Activities and Lesson Plans:
Poetry4kids.com
Funschool.com
Letteroftheweek.com
Eduplace.com
Teachers.net
Handwritingworksheets.com
http://www.essortment.com/in/Children.Education/
teachingheart.com
teachnet.com
teacherplanet.com
Just for Fun sites:
ClassicFairyTales.com
Junie B Jones (juniebjones.com- I think)
Claires.com
Suessville
Hello Kitty
EverythingGirl.com
Adoptme.com (adopt a virtual pet and take care of it)
For Toddlers:
Noggin.com
Nickjr.com
first-school.com
Winnie The Pooh (I think it's on the disney site)
and Familyfun.go is great from crafts, arts and fun recipes.
I don't know the direct links to all of them, but a google search will lead you there. I know how frustrating it is to lose all your information. As matter of a fact, I think I will write these down tomorrow, and some others I'm sure I'm forgetting.