I thought the Visual Studio designer and editor is all you need to create rich WPF apps, until I had to create a style for radio button with circular gradient on check mark. There would not be a problem (except the designer’s property tab sometimes does not want to work with resource dictionaries), since you can easily create linear and radial gradients in VS 2010 in property tab. The problem raised when I needed to play with other RadialGradientBrush properties, like Center, GradientOrign or RadiusX and RadiusY, which allows to create more glossy and cool gradients.
Online Gradient Maker allows to manually modify all gradient properties and has real time gradient preview. What is also very useful it can generate XAML and C# code, so you have also a way to create gradients programmatically.