Many of you are probably aware that google search works like a calculator if you type in an arithmetic problem (e.g. search for "2+3" and you will get 5). Recently, they added a graphing feature as well. If you search for something like "y=2x+3", or even just "2x+3" google will provide a graph of the function. You have the ability to zoom in and out, and there's an automatic trace feature for seeing the coordinates of specific points as you move your mouse over the function. You can graph more than one function by seperating them with commas. It won't solve equations (like Wolfram Alpha), but it's still a quick and easy way to get a graph, and with a screenshot you could easily get images to insert in your own worksheets or activities. Give it a try!
Jing is also a nice free program that is a little easier to use to capture parts of a screen.
There is also a Microsoft Math add-in to Word that inserts usable graphs that you can use in a worksheet.