If you hunt Green Bay and the Mississippi long enough, you can shoot quite a few species. Wisconsin has a lot of water, and pretty much all the same ducks everyone else shoots besides some of the sea ducks. As Loon pointed out, he has shot all the scoters. Lake Michigan has one of the largest concentrations of old squaw, so we even shoot most sea ducks here. There are rare times, people will even shoot juvenile eiders, barrows, and harlequin. Again, they are a rarity. I put snows in the same category. We shoot a few in Wisconsin, but this is generally not where they are. I have a real pretty ross that I shot a few years back that was with a group of cacklers.
I've shot just about everything that's here, but I haven't shot many of the odd ducks, but I haven't hunted the Lake much, and will certainly be back.
I've hunted the mississippi a lot, and have shot just about every dabbling duck and diver there is.
My list of Wisconsin birds are as follows. Unfortunately, the birds here pale in comparison to the birds of the south that get winter plumage. This is not the state to collect birds for taxidermy however. Not saying that none will look good, but a pintail (for example) shot in Texas in January will by far look way prettier than a Wisconsin bird shot in november.
canada geese (from tiny geese to the big boys)
and one ross