My vector xtGauge is a Raphael based jQuery plugin, is highly configurable and imao (in my arrogant opinion) it rocks. There are lot's of parameters you can set but the main settings are min, max, target and of course the currentValue. It also has an update function so you can update the display at run time.
Check this screen grab. I'm probably going to make it publicly available here shortly, after I've added some copyright/licensing info to the script file.

You'll see the gauge background shade varies depending how far or close you are to the target.
I'm also stoked because, thanks to Raphael.js, it even works in IE. Yes, obviously it works in Firefox (Mozilla), Chrome and Safari. Unfortunately Opera doesn't like it at all, but my immediate audience where it is used in an internal application at Unilever South Africa are restricted to use IE, so it had to work on IE. I probably won't worry about Opera, but maybe someone will fix this if I release it publicly.
So if this little baby looks useful to you, come back soon to look for the download.