I'm learning game programming using C# and SharpDX. What decent user interface libraries exist that I could use so that I'm not reinventing the wheel? I'm not using any particular engine, just cobbling together libraries such as Assimp.Net, Jitter and so forth. At this stage I'm not using MonoGame, XNA, UE4, Unity or anything like that. This is a deliberate choice based on what I'm trying to learn, so whatever UI library I choose would need to be usable from a raw C#/SharpDX/VS2013 environment.

I'm aware of Coherent UI, but they want $500 just for a personal license. Too much when I'm just learning, and their licensing seems quite intrusive as well. What other choices are out there? Googling didn't seem to yield anything useful or current.

There is GWEN.NET, a port (not binding) of original GWEN for C++. I only used C++ version of it, it's clunky a bit but under permissive license. It has a nice (but modest) feature set. You might also need to write own renderer and input (it's very easy) if you want to use it with SharpDX. Another plus is that it works in C++, C# and all graphics APIs and OSes more or less the same, so you will learn once and can use it anywhere.

Thanks I'll check them out!