Windows/Mac/Linux (AIR): Say what you will about newspapers, but the old grey ladies are laid out for quick reading. Cross-platform app (and web app) Readefine breaks any site or feed into column-split articles and easy access jumps to other posts.
Some sites splay just far too much, well, stuff on their front page to make you want to dig into any particular article, and some articles are laid out in text that's too wide or too intruded upon by other elements. Readefine takes the current article you're looking at and gives it the centre slot, and lays out the other articles, ordered by feed location, around your article on the edges. You can change the font, size and other layout aspects if you don't like the default, but it reads pretty well right from the get-go.
The app takes in RSS feeds, HTML or plain text sites URLs, as well as copy-and-paste text. The neat side feature is being able to log into Google Reader through Readefine and read your feeds inside it, moving from article to article with familiar n/p and spacebar shortcuts.