The background of the thermometer image (the part with the text labels on) can be customised to fit in with your site’s design. The height (or length?!?) of the thermometer can be customised, and the scale of the mercury bar will automatically adjust accordingly.
Also includes a widget for use on sidebars.
This plugin requires that the GD libraries are available within PHP.
Download and info; http://wordpress.org/extend/plugins/olimometer/