For only US$0.99, the OS X Farensius app is just adorable. It adds a current weather indicator to your menu bar, and offers an optional 5-day forecast in its drop-down.
It's exactly what I've been missing on my desktop. I have it set to update every five minutes, and with a tiny glance up and to the right, I can keep track of the current temperature.
Farensius is one of two related apps. Its big brother, Farensius Desktop ($1.99) adds the forecast to your desktop wallpaper. For me, my bland white desktop background is a necessity -- so I'm sticking with the basic app for now. Those looking for a whimsical we
