I think xoscope,
http://xoscope.sourceforge.net/or something like it would be interesting on a Collie.
I have used it on my powerbook in combination with
a homemade electromagnetic field detector that I plug
into my audio in port.
The screen on the Collie is a little small, and may pose
a problem in porting xoscope, but if sound in is working
(is it? I have not been able to record memo on GPE yet,
but that may be just my problem) this would be a great
device for acquiering all sorts of interesting low voltage
signals.
(EMF meter: some inductors, an opamp (optional if you
have enough inductors or big enough coil), germanium
diodes to keep voltage swing close to half a volt, an audio
transformer (also optional), a 1/8 miniplug jack, and
male-male cable.)