Garageband for iPad
There have been many postings about the new app, but here is a very quick review. At $5, you really don't have to think too hard about downloading this one. Compared to the Garageband for iMac or Logic 9, it is not as capable but as a sketchpad on the iPad it is hard to beat.

You get 8 tracks that you can create with loops, "smart instruments" and/or manually played keyboards, guitars, synths etc.
The best part of this app is the virtual instruments. The drums for example, let you layout drum parts on an x/y grid based on complexity and loudness - this is a very interesting method of putting a quick drumbeat together. You can also just bang out a beat repeatedly on virtual drums on the screen and record it.

Other means of creating tracks include playing a virtual guitar by chords, or by individual notes OR by individual notes constrained to a particular scale - noodling up and down the notes will always be in tune for the non-talented!

Similar functions are available for piano or keyboards. You can quickly hit chords or just play individual notes either on a keyboard or constrained to a key and scale. You can also use "autoplay" for most of the instruments where a given rhythm is played automatically for selected chords/notes.

For the more talented, you can put instruments (guitars, vocals etc) directly into the iPad and record tracks as well.

Garageband also comes with a few hundred loops that can be put into the tracks as-is. This seems like a limited first release in many ways, however. There isn't really a way to control the volume dynamically (i.e. fade-ins and fade-outs). There also surprisingly isn't a way to manually edit the notes on midi tracks unlike the iMac version - hopefully this will be added. Right now, there is no way to add loops or import WAV files without resorting to live recording.

Also missing in the initial release is the ability to transfer projects to the iMac version - a future update to the iMac version is supposed to fix this.

For now, my favorite all in one iPad solution remains NanoStudio but this is a good addition.