Gmail launched new exprimental features that show previews for some of the links included in an email for: YouTube videos, Picasa, Flickr links, and Yelp reviews. Just turn on previews from the Gmail Labs tab under Settings, and rather than having to click on a link to see, you'll see a list of previews below the message. Here’s an example, enable Youtube previews, and you can watch YouTube videos from inside your email: