most of what i did are prop to my customer so i can't post any of them here. But let's see what i did with 'till now

programmable audio patch board:
300 in, 300 out. saving patch cord and messy patch boards...

Custom Software dongle protection:
if the dongle is not installed, the software won't run... yeah i reinvented the wheel...

programmable power supply
16 outs (1 AMP), generate fixed or custom AC (+ variable dc offset), DC curves.
log each output current to the pc.
over-current protection

Analog & digital data logger

car radio decode dongle
for Blaupunkt, Porsche, Honda, Acura, Kia, BMW, Mercedes, Kenwood, Land-Rover, Audi, Hyundai, Mitsubishi, Toyota, Volkwagen, some GM and Volvo.

EEProm programmer

programmable and fix function/tone generator

multipurpose test and calibration jig

multi output programmable timer

and i know i forget some.

I have tons of other idea to do for my website... i just need some spare time...

Glad to hear you learned from the USBDemo.