This is pretty darn neat: http://www.wolframalpha.com lets you create your own widgets that you can embed in a website, Moodle page, blog, etc. I just put together this one that plots rational functions. You input the numerator expression, the denominator expression, the plot’s xmin & xmax, ymin & ymax, and voilà! it plots the function! Now my students can spend their free time investigating all kinds of pretty graphs.