Here are some sites that document how to do different things (since I always forget some of them):

• Daring Fireball Markdown
• MUD Markdown Cheat Sheet
• Markdown Help
• Markdown Cheatsheet
• Markdown Cheat Sheet

All are good and some have things others don't.

Some of the features I tend to want to …

Here is a site that has a maybe marginally useful utility (I'll see after I try it for awhile). mdless: Better Markdown in Terminal.