Educational Software
For social studies, it's hard to beat the oldie -Where in the US is Carmen Sandiego? It teaches a lot about the US. By providing the students with a form to fill out, you can monitor their activity and help them succeed. Playing the game with them a few times using the teacher station connected to the tv (or projected on a Smart Board, if your system is rich) makes it more fun for them and you. This program can sometimes be bought really cheaply: the advertisments say you are only paying the postage.
Sunburst Software has some really good programs 10 copies for $100. If you shared with another teacher, you end up with really low cost programs. One called How the West was 1+2X3 (or something like that) teaches order of operations in math in a really fun way as the train races the stagecoach.
They also have one that provides activities, puzzles, and and tests on many children's books on your level. I cannot remember the name of this one.
Edmark has 6 programs (castle, rainforest, ocean, Egypt, etc.) which provides the setting, character images, and props for students to create stories.
All these are older, low cost programs, that really are good. Some of them take extended amounts of time to play (you can save your project and come back to it) while there are others that can be finished in a brief time.
If you are a Mac user, I know lots of great ones that are free.