1. TweakyBeat
    Simple and brilliant little monophonic drum synthesizer and sequencer. The holy grail for some.
  2. Elastic Drums
    Unbelievably versatile, tough, and bizarre drum synth with cool effects and intuitive song writing capabilities.
  3. SeekBeats
    From the guy who makes TweakyBeat, a drum synth with deeper parameter control and a unique Randomizer function for great sound effects and performance possibilities.
  4. DM-1
    A rich and highly customizable collection of classic drum machine sounds and practical but interesting effects. Also comes with some unique libraries of pitched timbres, so you can write interesting melodies with this thing too.
  5. Impactor
    Amazingly well-designed percussion performance app with cool FM and granular synthesis backbone that works with the phone's microphone in a cool way so you can tap out rhythms. Great sequencing and sound flexibility.
  6. Figure
    Not exclusively a drum machine but too fun and clever to leave off this list. The easiest way to make a cool beat on your phone. Beautifully and intuitively designed.
  7. MoDrum
    Limited but useful 808-style clone. Rugged, beefy DSP.
  8. Flexy Drum
    Fun, noisy, and simple little synth-drum performance environment. Not a ton of flexibility but cool to play with.