Graphing functionality has just been introduced to Google. See the graphs of mathematical functions right on the search result page. Type a function in the search box and you’ll see an interactive graph at the top of the search results page.
- Zoom in and out and pan across the plane to explore the function in more detail.
- Draw multiple functions by separating them with commas.
- Extensive range of single variable functions including trigonometric, exponential, logarithmic and their compositions.
This functionality is available in most modern browsers. I've tried it successfully in both Safari and Chrome.