http://www.fretbase.com/blog/iphone-apps-for-guitar-players/
Fret Surfer Guitar Trainer
The idea behind this app is to help you learn all the notes on your guitar. The app has two game modes - finding the right fret given a note and a string and naming the note based on a fret. The games are customizable so you can focus on particular strings, sharps or flats. You can even play the games in alternate tunings.
iPractice
iPractice turns your iPhone or iPod Touch into a mini guitar tutor. The app is geared towards beginner and intermediate players providing a set of 170 individual guitar lessons to help you work on fundamentals and rhythm playing. iPractice provides the backing track and drummer so you can practice with a beat - an important part of any practice session. Priced at $2.99 it's cheaper than any book you'll buy at the store and much more interactive. This app is Fretbase recommended.
Pocket Tabs
Pocket Tabs allows you to download tablature directly to your iPhone or iPod Touch. Once a tab has been saved to your device it can viewed with or without an internet connection - handy for Touch users. The tabs available for download are listed on Pocket Tab's website. We've found the tab selection limited when compared to other major tab sites but users are adding new tabs all the time. Other features include auto-scrolling with speed settings, font sizes can be adjusted for better viewing and you can email tabs to a friend.