I love Black Sails so much! I've also seen North and South and I loved it. Deadwood sounds so interesting, I definitely need to watch it.

I'd say Downton Abbey, but... For me it got worse in the later seasons, by that point I liked reading the fanfiction better than watching the show. Still, I still remember it fondly and it had some great characters. I also loved the first seasons of Vikings, but I stopped watching shortly before they killed off my favourite character (I'm petty I guess).