Let me preface this by saying first: I'm not going to give you a thorough review of these apps. They're all in the app store. Read the reviews, try the free ones, decide for yourself. I just want to make you aware of some of the real, serious tools available to enhance your music experience.
There's a free version of this you can try. This is a good one for those of us who struggle a little with reading. You play a note, MagicStave shows you where it is on the staff. Nice writing aid!
A real chromatic tuner! You don't have to use a Guitar tuner any more! There are lots of these in the app store - I like this one.
This one has a pretty simple user interface, a metronome with a variety of sounds, etc. Useful.
This is one of those multi-channel studio recorder apps. I haven't figured any of them out yet, I have this one, StudioApp and Studio Free. Honestly, I usually just capture something with iTalk until I can get home and use Audacity. But a lot of folks can get good results with one of the ones I mentionsd.
OK, true confession time: THIS is the app that motivated me to post today. This might be the coolest thing on my iPhone next to Safari (or FaceBook!).
The app comes with 900 songs. Now wait - you don't get the lead sheets like you do in a real RealBook - you get charts like the one at left. BUT... you also get an editor where you can create your own charts, a web-based editor (for PC-users), a MacOS editor (downloaded from their site), a help-forum, and a place (accessible from your phone) where you can DL MANY more songs. Did I mention that the app transposes for you? Did I mention that the transpositions are available written for a C, Bb, Eb, F and G based instruments???
But best of all, you now get accompaniment! That's right, the app PLAYS the accompaniment (per the chart). You get a decent-sounding Piano, Bass and Drums to play along with.
Is iRealBook the ultimate iPhone-based woodshedding tool?
For the price of an iTunes album ($9.99) plus an upgrade to the "Jazz Styles Pack" (more rhythm motifs for your player for $5.99), this is the most powerful tool I can think of in it's price range. If you're a musician and you own an iPhone, iTouch, or iPad, I can't say it strongly enough: you need this app! (iRealBook is available for ANDROID too)