The Sigma EF-500 series flash is supposed to be compatible with the Dimage Z-series. I have talked with Sigma tech support and although it has only been tested with the Z1/Z2, I don't see why it shouldn't work with the Z3/Z5. I'm porbably gonna purchase one myself.
Sigma offers this flash for 5 different mounts in two models. Make sure you get the one for the Minolta mount. Also, the models are the ST and the Super. The flashes are basically the same, but the Super model allows a little more manual customization. The flash is also rated up to 165'.
Today's problems don't worry me,
I haven't solved yesterday's yet.