While researching some open source sites today for Language Arts, I came across this gem site called K-12 Resource Site. This is EVERY teacher's dream site - it has compiled lists of GREAT resources for various content areas from elementary to high school ALL IN ONE PLACE:)!! Simple choose a content area on the left hand side and you will get a plethora of websites for that area on the right with a short description of what that particular site has to offer - LOVE IT:)!!
I LOVE when you come across golden ones like this! Now I haven't looked in and through it, but the organization of the site is great, and the websites listed are familiar ones that I know are great!
Good luck searching here - just wish we had more TIME to do this, huh??