YoWindow (free, universal) is a cute and effective weather app for the iPhone and, now, the iPad. When we reviewed the app a few weeks ago, it was only available for the iPhone. The most recent release, version 1.1, is universal and adds support for Apple's Retina display.
Other changes you'll find in this update include a new docking feature that keeps the display illuminated while the app is running. That's pretty useful. Dock your iPad for a instant weather station. Also, the iPad version really emphasizes the animations that make YoWindow so charming. There are several themes to choose from, and each reflects the live weather outside your window.
Those looking for extensive weather information will want to look elsewhere, but if you simply need an answer to, "What's the weather today?" in a cute package, YoWindow is for you.