Many of these websites were obtained from Free Technology for Teacher a blog by Richard Byrne.
Web2.0calc is a free online scientific calculator. While it won't replace the TI-84 Plus, it can do what your average high school student needs it to do. The best part is, you don't have to use it on the Web2.0calc site because they offer three widgets that you can use to embed the calculator into your own blog or website. Click widgets to get the embed code to embed this calculator on your class website.