I've been a big fan of Battery Widget Reborn since we first covered it back in July of 2012. In fact, it's been installed on every device I've owned (or tested) since then. Why? Because it looks good, brings a lot of info to the table, and is constantly updated with new features.
One of my other favorite widgets is the more-recently announced DashClock Widget. There's a lot to love about it, too – like the fact that it supports extensions, making it infinitely customizable. Developers can easily add DashClock support into their app thanks to its handy API.