FL Studio Mobile HD
Click Here to Buy it Now from the Apple App Store, $20
The production software made famous by 9th Wonder, Soulja Boy, and Lex Luger is available for the iPad and iPhone (though, we recommend only using it on your iPad). You can do nearly everything you could do on the desktop version: All the FL Studio instruments, drunk kits, and loops are there, as are the drum pads, wave editor, a 99-track sequencer, and much more. When you're done crafting your masterpiece, upload it directly to SoundCloud or Dropbox.