"I need a drink. Where's the bubbler?"
This is perhaps the most well known Wisconsinism, though its origins are murky. The prevailing myth is that a precursor to the Kohler Co. patented the invention and trademarked the name "bubbler," but according to the company, that's just not true. Kohler did use the term to refer to parts of their drinking fountains, though. It may also have been popularized in schoolhouses around the turn of the 20th century, thanks to standard stoneware jugs that held drinking water. When you used the spigot at the base, air bubbled up, just like those water coolers in an office. Sounds like a plausible enough explanation to us, yah know?
"Can you pick up dat dere beer I like at Woodman's?"
A lot of Wisconsinites have a tendency to turn a TH sound into a D sound. It's especially prominent in older folks, and it's what turns up north into the ubiquitous "up nort'." This may stem from the heavy German language influence on the state, especially around Milwaukee.
"I'm at home yet so I'm gonna be late."
Around here, yet often means "still." One of the best sentences to a Wisconsinite's ear is, "We've got some Spotted Cow yet, yous want to come by or no?"