Fingerlabs' DM1 is a slickly designed drum machine app based around a familiar pattern grid.
Tapping a step activates the drum sound for that beat, and double-tapping will make the note louder. Patterns can be arranged into songs and you can toggle between song and step mode.
A swing function is available. A mixer offers control over each drum's pitch, level and length.
You can select drums from the 29 available kits for each channel as desired. Kits include classics like the Roland CR-78 and TR-909, as well as original stuff.
You can record beats in with pads, selecting between "add" and "replace" modes, and there's a nifty Repeat ribbon that allows you to trigger and record repetitions of a given sound.
The FX page provides a pair of X/Y pads and effects like Delay, Phaser, Texturizer and Robotizer. These last three are only available for iPad 2, however.
As of version 1.0.1, there's no sample import, AudioCopy or MIDI I/O, although all are promised.