Polar Bear supports GFM! The following text has been taken from this page.

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Emphasis, aka italics, with asterisks or underscores.

Strong emphasis, aka bold, with asterisks or underscores.

Combined emphasis with asterisks and underscores.

Strikethrough uses two tildes. Scratch this.

  1. First ordered list item
  2. Another item
    • Unordered sub-list.
  3. Actual numbers don't matter, just that it's a number
    1. Ordered sub-list
  4. And another item.

Some text that should be aligned with the above item.

  • Unordered list can use asterisks
  • Or minuses
  • Or pluses

I'm an inline-style link

I'm a reference-style link

You can use numbers for reference-style link definitions

Or leave it empty and use the link text itself

Some text to show that the reference links can follow later.

Inline code has back-ticks around it.

var s = "JavaScript syntax highlighting";
alert(s);

s = "Python syntax highlighting"
print s

No language indicated, so no syntax highlighting. 
But let's throw in a <b>tag</b>.

Colons can be used to align columns.

Tables Are Cool
col 3 is right-aligned $1600
col 2 is centered $12
zebra stripes are neat $1

The outer pipes (|) are optional, and you don't need to make the raw Markdown line up prettily. You can also use inline Markdown.

Markdown Less Pretty
Still renders nicely
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Blockquotes are very handy in email to emulate reply text. This line is part of the same quote.

Quote break.

This is a very long line that will still be quoted properly when it wraps. Oh boy let's keep writing to make sure this is long enough to actually wrap for everyone. Oh, you can put Markdown into a blockquote.