Biticker shows the Bitcoin exchange rates (in USD or EUR), and an updated chart of the selected time span whenever you need it.
The current exchange rate is always presented on the icon in the browser's top toolbar, and a click on it shows a detailed chart of the exchange rate during the selected time span.
More on http://www.biticker.com
#### UPDATES ####
Changed to Bitstamp's Web Socket API
Updates for the settings page
Added urls to permissions list
Reduced permissions level
Added support for "Log Scale" on chart + settings
Added bitcoin chart to the popup, with additional (configurable) settings to support it.
YAY! A new extension was born