The idea of a text-oriented mark-up scheme that renders as reasonably fancy HTML has easily spread from Wikis (and perhaps other early applications) to other low profile web content editors, such as blog software. Thankfully, it did so by going up a meta level. Textile and Markdown are two such schemes that are defined and implemented independent of blog/wiki/whatever software, and are easily integrated. I can't decide between the two, they both cover most of the bases. Textile gets extra points for justification (alignment) and HTML attribute (CSS classes, ID's) abilities. I like Markdown's link/image-by-reference syntax, though I don't know if I'd use it. Kudos to both for supporting multiple paragraphs and other things within a single list item, which drives me insane in most wiki formatters. (I often want to put code samples, such as steps to perform on a command line, in a numbered list, and many wikis will restart the numbering if I "leave" the list to enter code.) If anything, these systems will help put an end to the proliferation of reinvented hard-coded text-to-fancy syntaxes, and at least allow me to pick my favorite and use it everywhere.

Textile for MovableType, Textile for blosxom, Textile for MoinMoin Wiki. (Brad Choate supposedly integrated Textile and Kwiki, but I can't find a download.) Markdown's download package automatically provides MovableType integration, and Blosxom integration with very little effort.

See also Structured Text and reStructured Text, especially for co-mingling documentation and code.