Mac only: Previously mentioned web service Instapaper is well-loved, but if you've gotten used to keyboard shortcuts in web apps, userscript Instapaper Beyond will make you love it even more, allowing you to create a site-specific browser (SSB) rife with single keystroke actions.
The script only works with previously mentioned Fluid for Mac, unfortunately, meaning that you need to have a Mac and run Instapaper in an SSB if you want the shortcuts — a small price to pay, however, if you already have a Mac and are a keyboard shortcut hound. It has instant, one-key shortcuts for going to your unread, starred or archive folders, as well as archiving, starring or marking unread selected articles. It also comes with the standard page-navigating shortcuts (like scrolling to the top of the page or going to the next article in the list), and even has built-in Evernote integration, allowing you to clip to Evernote with one keystroke. Hitting the "h" key brings up a HUD-style list of all the shortcuts you can use.
To install the userscript, download it, and in your Instapaper SSB, click the script icon in the menu bar. Then hit "New" and copy and paste the contents of the script. Alternatively, you can just drag the downloaded userscript to your ~/Library/Application Support/Fluid/SSB/Instapaper/Userscripts folder, replacing "Instapaper" with whatever you've named your SSB.
Instapaper Beyond is a free download, works with Fluid for Mac OS X only.