Longform: Good, long journalism, 4000 words and up
longform.org
longform.org
A couple suggestions: I think the front page could be two to three times as long. Also, the "Read Later" button doesn't feel very button-y. My first thought was "Why does every article have a bookmarklet for me to drag to my toolbar?" It would probably be better as a link. Lastly, could the word "Instapaper" and the fact of the site's integration with it be more prominent? I had to hover over a Read Later button to figure out what would happen when I clicked it. (I suspected that it would save to Instapaper, but that's largely because of the aforementioned bookmarklet-ish look.)
I second ihodes' sentiment that this is not far from being something I'd pay for.
Edit: on second thought, I'd only multiply the number of articles per page by 1.5–2.
Perhaps a simple tagging/categories mechanism, crowd-sourced or by the editors. Sometimes I'm in the mood for a certain type of article, and having the simple recommendation that it's of the "US/National/Politics" genre is enough to make me hit "Read Later" when I otherwise wouldn't.
A nice layout, as well. Kudos!
Also, were it to be extensively curated and organized, perhaps with 1 sentence blurbs about the articles, and frequently updated, I'd pay a nominal fee for it, if that's a direction you'd be interested in going with it.
http://www.brandonsanderson.com/article/56/Splitting-AMOL has a description of what happens when a book gets too long (400,000 words)