I haven't, so far, mentioned any subscription or fee-based services, because something seems wrong about teachers spending money in order to do their jobs. Nevertheless, there are a few for-cost teaching tools that I use and find to be worthwhile. Chief among these are the streaming-video databases at Brainpop and Discovery Education. As they say, a picture is worth a thousand words, particularly when teaching science and social studies. And besides, kids love movies.
Brainpop was designed in 1999 by a pediatrician who needed to explain tough concepts to little kids. The site has hundreds of short cartoons based on state content-standards and searchable by subject or grade-level. Each video features Tim and Moby, a boy-robot team devoted to answering tough write-in questions. After a 2 or 3 minute cartoon, topics like mitosis and the law of conservation of mass seem strangely and wonderfully clear. The site also has videos for junior brains, Spanish-speaking brains, and an entire menu of free movies. There are also many brainpop videos available through McGraw-Hill's textbook companion sites for physical science, life science, earth science, algebra, and others.
Discovery Education is the offspring of Discovery Communications, the non-fiction media company. Their site is jam-packed with resources and products, but the gold-mine is inside their program, DE Streaming. This program has thousands of videos including The Magic School Bus, The Standard Deviants, and lots of Discovery Channel-like videos to help teach topics from the 1964 World's Fair to the water cycle.
Many districts already subscribe to these services, and all you need is to find out the password from the librarian. Lots of other principals and administrators can be convinced to purchase subscriptions once they've seen the sites. And, if you can't subscribe, both sites have free trial subscriptions.
Images from my collection, Brainpop and Discovery Education