You have a couple of options:
1) Alpine Valley (south of Milwaukee, near IL border)
2) Cascade - further north on I94, near Wisc Dells(maybe 1.5/2hrs drive)
3) Devil's Head - also off of I94, near Wisc Dells
4) Granite Peak (?) used to be called Rib Mt. - near Madison I think
I've been to the first three (used to live in Northside Chgo, now in Minneapolis) and would recommend either Cascade or Devil's. I haven't been to Cascade in about 8 yrs but was at Devil's Head over President's Day weekend just after they got hit with 5in of snow - so, it was fun but Wisc standards. If I remember correctly Cascade has steeper runs but Devil's runs are longer in general. If you want decent steep at Devil's go towards the runs to the far right of the hill.
Cascade overlooks I94 and had (back then) had frugal ammenities whilst Devil's is more secluded and has a more "resort" feel to it (ie: on site lodging, outdoor hot tubs, outdoor firepit, etc).
Alpine Valley is closest to Milwaukee, maybe 20-30mn drive and it the smallest of the four; so if you're short on time, it's better than nothing.
Hope that helps,