I don't think this one is already in the list:
The PNY Technologies Europe 64A0TNDYA8G17 1GB module seems to be working ok in a Duo.
It's passed two memory tests so far (I'll run some more). [UPDATE] Three now.
Frontview reports is as 1024 MB [2.5-3-3-7], so timings are the same as the 256MB that it was shipped with.
I'll run some file transfer tests and update this message with the results.
Results Read : 28.7 MB/s, Write : 30.9 MB/s --- for a 4GB file.