If you were teaching a programming course, what language would you teach it in?

Depends on the target audience

For people how intend to become computer scientists and/or 'serious' programmers: Haskell

For people how are simply looking for a job in programming: C# or JavaScript

For people who don't want to become programmers, but just want to use programming to make their life easier: Whatever scripting language their main work application uses, or Python as a good general language

Depends on if its just an intro to programming course or part of the backbone of a full degree. Either way thou ML appears to be a compelling choice.

Python. Easy stuff is easy. More complex stuff is available. Nowhere near the amount of hacks you need in JavaScript.

JavaScript for beginners, Haskell for advanced.

Groovy here. Just because I know it reasonably well, like it a lot, and it's a convenient part of the overall JVM ecosystem.