Matt & Kim.
From humble origins (effectively started because one of their friends needed a band to open for another band), Matt & Kim have been surprisingly successful. They manage to make surprisingly addicting songs for people with little to no formal musical training.
On top of that, they are famous in the entertainment community for their shows' high energy and fun.
A few songs I recommend checking out: "Good for Great", "Where You're Coming From", "I'll Take Us Home" and "Daylight".
Side note, most of their songs are pretty easy to learn, so they're good if you're just getting started on an instrument. "Daylight" was the fourth song I learned on accordion.