For the best of Science on the web, check out Sparticl
I just read a great review of a handy (and free!) resource that curates the web's best science websites, information, videos, and more. Sparticl is geared toward middle and high school students looking for a one-stop-shop for hand-picked and high-quality science materials.
This looks like a welcome addition to any science teacher's toolbox. With its screened materials, easy to use format, and great price (did I mention it was free??), be sure to bookmark this one.