the entire tom barrett series of interesting ways to use: twitter, wiki search enggines, voicethread, prezi, google docs, interactive whiteboard, google earth, & wordle inthe classroom
Line of best fit applet. Plot up to 50 points, you "guess" where you think the line of best fit is, a thermometer shows how well you have done, then you can click to get the line of best fit, get the equation with the slope and the y intercept. Only in the first quadrant though.