Most people have noticed that GMail is offering an RSS (Atom, technically) feed. However there seems to be some belief that it is not fully available yet. Fools! Instructions (especially for Firefox users) follows.
If you want to make the GMail Atom feed available in firefox, there are a few steps you will need to take.

• First, click the "Live Bookmark" button (orange, lower right)
  
• Add the feed in the location of your choosing (I suggest in your bookmarks toolbar folder
  

Now, you must edit the bookmarked URL.

• Click bookmarks
  
• Click Manage Bookmarks
  
• Choose the GMail feed
  
• Right Click GMail feed, choose properties
  
• Edit "Feed Location" like so:
  
  change from "https://gmail.google.com/gmail/feed/atom" to
  
  "https://username:password@gmail.google.com/gmail/feed/atom"
  
  Where username and password are...you guessed it
  
• Refresh the feed, and Ta-Da!
  

You should now have your unread inbox messages (and a brief description) available in your Live Bookmarks. This should work with other browsers/feed aggregators.