Tune-O-Matic > online gitar tuner

Now, truly, no one has an excuse for playing an out-of-tune guitar. howtotuneaguitar.org features a Web-based interface for tuning, and step-by-step instructions in case you’re really a newcomer. The tuner itself goes well beyond the basics, with support for Standard, Drop D, Open C, Open G, Open D, Open G, Half Step Down, Full Step Down, Open E or Admiral tunings. Powered by Flash, you can trigger looped recordings of the strings one by one.
read the full article at the Create Digital Music