My little list of things:
PC PS/2 keyboard to Amiga adaptor, for my CD32 and my A1200.
I built a simple IDE expander, it was a little unreliable though, so I bought IDE Fix and all works well.
I've done the A1200 timing fixes on 2 motherboards.
I built a sound sampler 10 years ago, worked kinda crap due to taking too much power from the parallel port, oh and {bleep} loads of cross talk/mixing analogue & digital grounds.
I towered my CD32/SX32 once. Blew up the keyboard port doing it though. Due to problems with the video interface, this did not last too long though ;(
Adapted an ATX PSU to power my Amiga and built a plug-in adaptor.
Built a teletext decoder from the design on Aminet, it still works!
Designed a 24 bit I/O card for the Parallel port. It worked OK, shame I lost the Amiga S/W in a hard drive crash. Also re-designed a variant for the clockport. Both had PCBs built.
Built an Audio mixer, 2 x line level and 2 x amplified inputs.
Tried to make a PC HD floppy work in my Amiga but no success.
Blew up a CD32 trying to increase the video brightness, damn current mode DACs!
Replaced the capacitors on my A600 that cause the audio to fail. Replaced the PSU capacitors on the CD32 that are inserted backwards.
Currently in the CAD tool (I don't have a drawing board

) are a clockport adaptor and a scandoubler. Towards the end of this year by the time they are ready.
I've also built a few PIC and EPROM programmers from Aminet designs, all worked OK.
I think that's about it.