Has anyone found any decent iPhone applications for guitarists?

I've got a couple, a few with chord charges and scales, but haven't looked a huge amount into it.

Was hoping for a heads up or something...

My guitar teacher had a guitar tuner on his.

There's a four track portable studio (called Fourtrack) that you can buy and install.
http://www.sonomawireworks.com/iphone/fourtrack/

This looks very useful! Thanks!

This is a great tool, many time I get a melody when I am outside, and then I have to sing it (silently ) until I get home

Thanks for sharing this

there is an app for the iphone called karajan that I got a few days back... it is basically an ear trainer that can be set in a lot of different ways to test you in hearing intervals, chords, scales, pitch, tempo, and key signatures. you can also set it at different difficulty levels.. however there are a few parts of the app i've yet to figure out; like.. what I should select for the 'base note' and the 'play mode' at the main menu.