I rewatch The Wire once a year. I used to rewatch House every year or two, but it's becoming less regular now.

Otherwise, I've rewatched a bunch of other shows, but don't do so with any degree of regularity. I've rewatched Game of Thrones and Sherlock each once, but those are still too new for it to be a regular thing yet. Other shows I've rewatched within the past couple of years: Firefly, Buffy, South Park.