GSam Battery Monitor estimates how much time you have left on your battery with current usage, and gives you a nice graph with an extrapolated curve down to the projected 0% time.
Here's 3 more so you can pick and choose: Battery Widget (which comes with icon packs so you can choose how it looks on the notification bar); Battery Widget Reborn, which has a Dashclock extension, and Circle Battery Widget, which is simple but gives lots of info.