Not counting shows I abandoned in season 1
Luther (season 3)
Modern Family (season 5)
Secret Diary of a Call Girl (season 2)
True Detective (season 2)
Castle (season 2)
Glee (season 2)
Homeland (season 4)
The Big Bang Theory (season 5)
Unbreakable Kimmy Schmidt (season 2)
And those are only the ones I've definitely dropped, I'm not counting stuff like Buffy which I do intend to finish at some point (I stopped early in season 4). I'm a bit of a completionist, I even stuck with Dexter through the end just because of my deep affection for the first two seasons (and I even liked season 5, kinda, not anything after that though).
I'm curious about people abandoning The Wire in the middle of season 3, that's such a great season !