I've put together a free resource for anyone who wants to try it out. It's called "The eLearning Narration Tool Kit." It contains a series of phrases that commonly pop-up in eLearning scripts, plus a few course-specific introductions that you may find useful. The categories include introductions, scenarios, course review, and there's some quiz-specific verbiage as well.
It's a free download, and yours to use however you see fit. Perhaps you'd like to add a different voice for various places within an existing narration, or maybe you want to experiment with adding narration to a course...or maybe you just like free stuff.
Whatever your motivations, I hope you find this a useful resource. You may download it here:
Enjoy, and happy designing!