Another option is WindowsKey-D, which leaves up widgets for me, but makes zoomer (but not my tabbed) docks disappear, and reappear.
I created a widget, The Hardest Button To Button, to address this issue. You can get it here:
WWW Link">LinkI hope that isn't one of the widgets you tried already.
CerebroJD also has a widget, Window Command: [link="https://www.wincustomize.com/ViewSkin.aspx?SID=1&SkinID=643&LibID=34&comments=1"]WWW Link
As Bichur said, the standard "Show Desktop" shortcut in the quick launch area actually brings a special window, the Desktop Window to the foreground. This means it places itself above everything else, including the special Layered Windows that our widgets and other things reside in. In contrast, the widgets above actually minimize or otherwise rearrange the normal windows, and leave other non-standard display components alone.