Google Chrome: Lots of sites (including us) have truncated RSS feeds, only allowing you to see a portion of their articles in your newsreader. If you prefer to read the full articles, this extension expands them in full inside Google Reader.
After installing the extension in Chrome, some of your feeds will have an orange "G" icon next to their headlines. If you see this icon, it means that truncated article can be expanded by hitting the "z" key on your keyboard. It doesn't necessarily work with every RSS feed out there, but the database is built such that you can add sites to it as long as you understand xpaths. (Even if you don't, plenty of other people do, so support for more and more sites will likely grow.) I found that it worked with quite a few of my truncated feeds, although I couldn't get it working with Lifehacker — though the tipster that let us know about this extensions says he uses it for Gawker sites, so let us know in the comments if it works for you or not.
Firefox users looking for similar functionality can try either the Google Reader Preview Enhanced userscript or the Google Reader Full Feed Changer userscript. The first will open up a preview of the full article (from the site itself) in the Google Reader window, and the latter requires you to know xpaths and add all your sites individually. So, neither has quite the same out-of-the-box functionality as the Chrome extension, but at least there are some options.
Google Reader Full Feed is a free download, works wherever Google Chrome does. Thanks, Adam!
Google Reader Full Feed [Google Chrome Extensions]