Simple from the thread title. What was the last television series you watched on DVD (and the season/series number, if applicable), and which have you been watching currently, if any?
The last one that I watched was 24: Season 8. I'm a big 24 fan and I thought it was a great end to this series. DVD set had some nice special features too, including extended episodes and a look at the making of the New York CTU.
Currently watching Red Dwarf: Series One. I was heavily into Red Dwarf, back when it was airing on PBS in the United States, but I never actually saw the first series. I'm familiar with the mythos from the novelizations, but this is the first time actually watching it from the beginning. Great bonus features on this one too, including cast commentary on every episode (and crew commentary for the first one as well) and many other goodies and Easter eggs.