I use the Golden Ratio (ϕ, φ) so, so much in my design and layout work that I find myself bringing up a calculator to get golden dimensions basically all the time.

To make things easier for myself, I wrote a simple Golden Ratio Calculator yesterday evening. I used Dojo Toolkit. It's got a slider that affects the size of a+b, and three number spinners for a+b, a, and b that will affect the other three when changed.