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.
Give it a whirl! It's licensed under Modified BSD, so feel free to use it any way the license allows.
Now, here's Jurassic 5 doing What's Golden.