1) Hart Heartworks: Let's get it out of the way first: A division devoted to manufacturing and developing components for artificial hearts would be a dream for Jonathan Wagner because it would enable pun opportunities every single day.
2) Hart Colonics: Let's get this one out of the way, too: Can't you imagine Jonathan grinning just before a commercial break and telling Jennifer, "Well, our problems are behind us now"?
3) Hart Inkworks: The Harts open a series of seedy tattoo parlors across the region. Why? "Diversifcation," of course. When shady happenings are reported at the flagship, Jennifer has to go undercover and request a giant back tattoo of Jonathan. We find out that Max already has several--not all of Jonathan.
4) Hart Sports Enterprises: A company to organize the professional sports franchises the Harts own. Since I am making this list based on what I wish I could see on the show, I say give the Harts a Major League Baseball franchise circa 1982 or so. I don't mean have Jonathan buy one, I mean I want him to already own one but just mention it in passing because it's needed for a plot that week.
And to up the ante, have the Harts worried about a drug smuggling ring involving the clubhouse and the team mascot, and have them go undercover to ferret out the details. Naturally you have Jennifer be a hotshot "free agent from nowhere" and Jonathan the mascot.
5) Hart Back Alleys: This underexplored part of the company is responsible for creating noirish backdrops that give the Harts opportunities to don trenchcoats and talk like Bogart and Bacall.