Mediawiki syntax is incredibly easy to use and kind of genius. It would also work well with wiki posts. It also seems to be more familiar to non-developers than Markdown but I could be very wrong.
Examples:
==header==
===subheader===
====sub-subheader====
*bullet point without needing space
‘’‘bold’’’
‘‘italics’’
[[File:easyfilereferencing.png]]
[[File:easyfileformatting.png|300x300px|right|caption]]