The current version of
Agua also comes with an open state. David Lanham has an eye for detail, that's for sure
Some older sets by other icon artists have this as well, but beyond the
Icon Factory 200th set (modded it for myself on OS 10.3, so I know it definitely does

) I can't think of any that I know have the open folder state
for sure. Minium might possibly have them, since that is also a fairly thorough set? I think you could only get at them in the older sets if you exported icons from the prepackaged CandyBar icontainer, and I didn't usually download the icontainer version of icons if I already had the standard copy-and-paste icons so I didn't usually have the "open" folder
Leopard makes it really easy to swap icons because they're regular ICNS files instead of part of a single resource file, and the "open" folder is amongst the main folder icons, so hopefully we should be seeing some more sets that do this
