I'm a great fan of Markdown. It's an easy way to get formatted text into different documents in a consistent way. Github and Bitbucket use it for their README files, Ghost use it for their blogging platform, Trello for task descriptions, and the list goes on.
One of the main advantages of Markdown for me is that it is a plain text format that can easily be cut/pasted around various places. So you might start with the text in an editor, maybe sublime text, and then move it into Trello, or vice versa.
I'm using Evernote more and more these days, and it doesn't support Markdown directly, however, there are ways to use Markdown with Evernote. The two I have found most usable are:
Markdown here - by using a hot key (ctrl-M) you can switch the Evernote editor between Markdown view and formatted view. This works pretty well, but things can get messed up if you make edits in the formatted view.
Marxico - this is a cool app that works in parallel with Evernote. It can run in the browser, or as a Chrome extension. You edit notes in Marxico and sync them to Evernote. It's easy to select a notebook and tags. Marxico integrates with your Evernote account and flags each note with a red banner to click to edit the note. I'm using this in preference to Markdown Here now because the editing is more reliable and the tool is better integrated with Evernote. You'll have to pay a small annual fee to continue using it after 10 days, but I think that is well worth paying.