Suppose I wanted to create an open source WPF project written in .NET. I don't have a copy of Expression Blend, nor do I have the skillz in graphic design to make my own controls that look good. I love Developer Express' controls, but they cost an arm and a leg and I don't see how their per-developer licensing would make it possible to use them on an open source project.
What options are there for third-party WPF controls to be used in an open source project?