If you're neck-deep in math work, or just nostalgic for the high school days of your TI-83+, fire up the big G: it'll now serve you as a graphing calculator. Time to make sine waves!
It's pretty simple—plug in your formula of choice—say, x/3, (x/2)^2, ln(x), cos(pi*x/200)—and explore your graph a la Google Maps. Zoom in, zoom out, calculate. You just saved yourself a hundred bucks or so, and Google took a step closer to Wolfram Alpha. Both good things! Plug away. [Google via SearchEngineLand]