The Borgias and the Tudors are both high-quality, historically-themed series.
Other than that, Rome and Game of Thrones are probably the best TV series I've seen, followed closely by Twin Peaks and Season 4 and 5 of the original Transformers animated series from the 80s ( Soundwave superior, Michael Bay inferior ).
Walking Dead and Battlestar Galactica are also pretty good, zombie survival and sci-fi respectively.