Web Guitar Tutor

If you are an iphone or ipod touch owner, then there are a few useful apps available for musical training.  I'll list a couple I use regularly:

Karajan Ear Trainer
This is far and away the most bestest, most usefullest iphone apps I have found for any purpose.  It is also one of the most pricey, at $15, but I find it to be worth the money.  It plays not only simple intervals, but also chords (triads and 7th and more), scales, single pitches and even BPM.  It has a a few different sounds, a nice layout that has an actual keyboard in landscape mode, and a report on your progress.  You can customize the program in many ways, very easily.  Highly recommended for both beginners and advanced players.
www.karajan-eartrainer.com/en/

iReadMusic
This app is a really solid tool to help learn to sight read traditional notation on the guitar neck.  It has several modes, I use  'Play that Note!'  In this mode, notes on a treble (or bass) clef are displayed on top, and the fretboard is displayed on bottom.  The frets are a bit tiny, but it's actually precise enough to go through entire scales.  The program has a lot of customization available, including other instruments (piano, bass and banjo), sounds, and types of drills.  It's only $2, so I think it's worth the investment.
www.glpsoftware.com/

Metronomes and Tuners
There are dozens of metronomes and tuners out there.  I found two for free (my usual pricepoint) that work well.
iTick
Guitar Tuner
Tuna Pitch is a $2 tuner that seems to do the job.

GigBabyFree!
How is it that my wallet-sized phone can house an entire four-track recording studio?  People over the age of 30 may understand my wonder.  In any case, here is a free recording app that has 4 tracks and some bells and whistles to boot.  Really fun, and others like this get to be more expensive.
www.iometics.net/GigBaby!/