We are writing a complex rich desktop application and need to offer flexibility in reporting formats so we thought we would just expose our object model to a scripting langauge. Time was when that meant VBA (which is still an option), but the managed code derivative VSTA (I think) seems to have withered on the vine.
What is now the best choice for an embedded scripting language on Windows .NET?
The PowerShell engine was designed to be easily embedded in an application to make it scriptable. In fact, the PowerShell CLI is just a text based interface to the engine.
IronRuby as mentioned above. An interesting project to me as a C# programmer is C# Eval support in Mono. But it's not available yet (will be part of Mono 2.2).
My scripting language of choice would be Lua these days. It's small, fast, clean, fully documented, well supported, has a great community , it's used by many big companies in the industry (Adobe, Blizzard, EA Games), definetely worth a try.
To use it with .NET languages the LuaInterface project will provide all you need.
Why not try C#? Mono has a great new project especially for dynamically evaluating C# :
Another vote for IronPython. Embedding it is simple, interoperation with .Net classes is straightforward, and, well, it's Python.
I've used CSScript with amazing results. It really cut down on having to do bindings and other low level stuff in my scriptable apps.
I've used Lua before; in a Delphi app but it can be embedded in lots of things. It's used in Adobe's Photoshop Lightroom.