check out these mini trackballs

[midgetfidget]

http://www.sparkfun.com/commerce/product_info.php?products_id=755

These could be usefull on a midibox, I wonder if they put out the standard mouse signal?

[Wilba]

Standard mouse signal? If you mean something you could plug directly into a PC, then no.

The signal isn't compatible with rotary encoder handling in MIOS, but it would work as a controller for increment/decrement buttons with no extra coding... I suppose you could code your own support for it in MIOS so it could replace a bunch of encoders in a project... (I wonder whether 16 of them in a MB-SEQ would work... hmm...)

It's a pity that sparkfun don't sell the version with built-in LEDs!