Vatanator is a drum machine for iPad.
It comes packed with 140 built-in presets, and ability to add your own samples. There is an advanced MIDI integration, MIDI learn function and option to save your project for further use.The interface is simple yet one can dive in deep in the options.  It has two main modes where you can play with the pads or arrange a pattern and additional menus for effects, mixer, and song arrangement.