Forgive me if there's already been a discussion on this, I searched "markdown" and got an absurd number of topics.

I keep looking for the nice "markdown" syntax page when I'm typing an answer and I can't find it easily in the FAQ, or on the sidebar. I realize it is linked to on the "how to ask" page (which is how I eventually keep finding it), [and now that I'm testing out editing, I realize that the big blue question mark on the formatting bar also goes that page... so I feel pretty silly now] but I think it would be helpful if it were linked to on the sidebar, or perhaps if there was a text label on the formatting bar too.

The sidebar on the page for asking questions does have a helpful list of commands and a link, so perhaps that should be copied onto the answer page so that it is visible when writing an answer.

The flipside of this is that perhaps the interface will be slightly more cluttered, but that seems like a minor price to pay for better-formatted questions and answers.

One problem with googling for "markdown syntax" is that there are several different versions of Markdown out there and the one you find (I don't know) may not be the one that is implemented on MO. Indeed, they have their own special version (can't remember the link off the top of my head). The differences probably aren't substantial, but may be significant. So a local link is certainly better than everyone googling it - though whether or not it is sufficiently better to warrant cluttering up the display, I don't know.

The original Markdown was written (in Perl) by John Gruber, and that's what's on the Daring Fireball website. Michel Fortin adapted this to PHP, and extended it. The port is called 'PHP Markdown' and the extension is called 'PHP Markdown Extra'. This forum almost certainly uses 'PHP Markdown Extra', but not the most recent version of it. Andrea Censi wrote a Ruby version of PHP Markdown Extra, and extended it yet again. This is called maruku, and is what Instiki (and so, in particular, the nLab) uses. Maruku has the capability of interpreting mathematics (via some external program/script). I've backported that to PHP Markdown (Extra) and that's what the nForum uses. Stackoverflow forked their own version of Markdown, presumably to fit their needs a little better and that's what Mathoverflow uses. There are, no doubt, other versions in other languages all over the place.

So, yes, it's a little complicated ...

However, all implement the basic syntax which is on the daringfireball website. So if that website says that something should happen, it's almost certain to work in any implementation. I say "almost certain" because there are some edge cases where people have made different decisions on which way they should go (for example, we can't write Ti_k_Z correctly here).

Where should there be a more prominent link? One problem is that it's surprisingly hard to see anything that isn't directly in front of you. I think most people never look at the sidebar (I know I don't), so I'm hesitant to clutter it any further.

It actually IS prominent. Still, I never realized it was there...

I also have a hard time finding the description page whenever I need it, and I strongly support bbukh’s point 4.