Nice 1x1 battery widget. It doesn't drain battery as it stops working when phone's screen is off (proven to work optimally on Android 2.2). Combine it with Quick Settings (to get access to system settings) or with another app.
To open press Home -> Menu -> Add -> Widgets -> Quick Battery. Enjoy!
Author: Sergej Shafarenka
Market link: com.bwx.qs.battery
Web site: http://code.google.com/p/quick-settings/
Market downloads: >250,000
Market rating: 4.3 / 5.0