Linking to other Wiki pages on GitHub?

Using the Markdown link syntax

[Link Text](WikiPage)

seems to work in the edit preview but not on the actual wiki page. At least for me the generated link is WikiPage instead of wiki/WikiPage and I get the famous GitHub 404.

However the MediaWiki syntax

[[Link Text|WikiPage]]

works for me, even for Markdown wiki pages.

The internal-ref part is relative to your project. For wiki pages use:

[Page Name](wiki/Page-Name)

In the preview the link will be broken but when the page is saved it will work.

GitHub by default uses Markdown syntax for the wikis so you can just do:

[Arbitrary Link Text](Wiki Page Name)

Check out Markdown and this blog post for more information about their wikis and the other markup syntaxes they support.

This solution has issues when you're on the home page because it creates relative URLs. Check out Sven's answer, below.