I know of three main languages used commonly in the greater programming and tech community: Textile, Markdown, and reStructuredText. All three can be learned in a couple of hours or "winged" with the cheat sheet nearby.
Textile
Used by Redmine and the Ruby community
113 questions currently tagged on Stack Overflow
The most similar to HTML, but least readable source
Easiest nested lists of all three languages
Not understandable to non-programmers or the HTML-ignorant
Ideal for complex short documents (with links, nested lists, code, custom HTML); for example: short documentation, how-tos, blog or CMS content
for documentation?
how about doxygen?
I've use it for some of c/c++ project that I need to documentize.
Even you can 'abuse' it just like doxygen author uses for doxygen documentation
As you can see, it started with "how can I make a secure blog" - i.e. one that generates static HTML, and I found myself ensnared in markup languages, templating systems, etc.
Update
I refocused only on LWMLs with python implementations, and theyre here:
So far I've tried markdown and ReST, and I like the latter better for anything but
HTML snippets embedded in other pages. Tables, cross refs, indirect links, etc...
The Wikipedia page on lightweight markup languages has a good comparison between the various options, as well as showing syntax for common uses (headings, bold, italics, etc.)