Since it's allowed in HTML to not close <li> tags, lists are pretty readable and easy to write:
<ul>
<li>Item 1
<li>Item 2
<li>Item 3
</ul>
Haml is also great for writing <table>'s.
Markdown is for publishing, whereas Haml is for designers/developers. The point of Markdown is that non-technical users can use it, and it generally looks good and self-explanatory even unrendered.