I really like the cube shape that TinyDuino can take (I already made a cube-shaped GPS) but I'm still missing some output display.

OLED display was commented earlier before but they draw too much current for a coin cell, plus the smallest one I can find is 30mm so it won't fit anyway.

Still I think it could be nice to play with a small, 8x8 SMD LEDs matrix array in a TinyDuino shield as output as a display.