Animated Gauges With HTML5 Canvas: Gauge.js
The script is standalone (jQuery is supported but not required) and doesn't use any images or CSS.
It has 2 built-in interfaces (both looks very nice) and responds very well to value changes by animating the gauge.
There are options to set the animation speed, default/min/max values, colors and more.
To sum up, Gauge.js is a very handy script to visualize regularly changing (live) data.