I want a service that will host content that is searchable, categorizable, and organized around answering questions that internal users create. A CMS for FAQs, essentially.
I also strongly prefer the following features (in order of preference):
The service allows me to embed videos.
The service allows me to upload pictures.
The service provides a means to search questions.
The service uses Markdown as its input format, preferably as its preferred input format.
The service costs money. (See, e.g., here for why that's important.)