String pluckers listen up. Here is something you might be interested in. The PocketGuitar is a virtual guitar for the iPhone and iPod Touch, developed as a Google Code project by a guy called Shinya Kasatani.
Via 
You can also use the songs on your iPod
for those long guitar sessions. To install, launch the Installer,
choose Sources, and add http://podmap.net/apps to your repositories.
Look under the "Toys" category to find PocketGuitar.