Online Markdown editor
I’m really not a fan of Markdown, as I’ve been used to MediaWiki syntax, BBCode, or even more simply, plain HTML (HTML is so trivial, I don’t really get why so many people feel the necessity to invent their own markup language over it…). But with Github’s quasi-monopoly on easy Git hosting (I personally like Bitbucket though – but they use Markdown too) it seems to become kind of a necessary evil.
Dillinger.io provides an easy way to edit your markdown readmes, with a simple and efficient interface: code to the left, “what you see is what you get” (just a non-editable preview) on the right. It lacks a syntax help, but the provided example document already has plenty of the useful syntax and you probably won’t need more than that.