I run a popular guitar teaching site and I want an online tuner that works like the one on this page: [url removed, login to view]
It's a chromatic tuner, which means it reads any note, not just the 6 notes that guitars are tuned to. You can see that it is picking up the frequency of the notes played by the user, and the horizontal bars at the bottom move to the right if the note is sharp of the nearest pitch (the big letter), and move to the left if the note is flat. When they stay still, you're in tune.
The one on the page is copyrighted, but there are many ways to display the info. I could send my idea of what it should like to anyone interested. There are countless hardware tuners on the market that do this, but I've only ever seen one online version.