Polynome app for iPhone and iPad

Polynome is an iOS 4 and later app that allows you to visualize and hear complex rhythm patterns. You can set up to 4 individual rhythms, each being from 1 to 11 beats per measure. You can adjust the tempo (beats per minute) from 20 to 220. For each line you can set the following:

On or Off

Beats per measure
Note that the first enabled line is what the tempo refers to.

Sound stage - Stereo or Monaural
Stereo sounds pan from left to right.

Color of light

Click sound
You can add a custom click sound via iTunes and then use it for one or more lines.
The sound can be theoretically any type, but it is recommended to have it be a 2 channel, 44100 Hz caf file.