See that there? That's the Weather Flow app. And that's pretty much all there is to it. Simple, easy-to-read data like date and time, temperature and forecast (daily or hourly). Don't overthink it. The backgrounds (which pan ever so slowly) are gorgeous.
There's a typographic theme (available in black or white) that you can switch to in the settings, and there are a couple 4x1 widgets available (we've got screen shots of both after the break), but really what you see above is where the money's at. It's extremely well done, and it's currently going for $1.99. We've got download links after the break.