The spirits continue to get much needed love in this next card from Dark Ascension:
A limited-time-only, mini-Back from the Brink.
--But wait. Upon further inspection, in all those lines of text a very important keyword is missing... Seance doesn't give haste to the creatures is brings back for single turns! Upon even further inspection, Seance brings a creature back during each upkeep and not just yours. Very interesting. This card is definitely built for a black/white creature heavy sacrifice deck. If you don't have a lot of creatures, your graveyard is going to dry up quick. And if you don't have a sac outlet, the creature you bring back on your turn is going to be completely worthless (if it doesn't have haste). On its own, because it's so limited, I'm going to say that its much worse than both Back from the Brink and Moorland Haunt.
This one's a little tricky. You could always go for my all time favorite sac outlet and bring in a pair of Diamond Valley(s) and just get free life gain, but that's not too interesting. I think I'd be much more interested in giving all your creatures haste with something like Fires of Yavimaya. That's almost interesting. But if you're going to use something as narrow as Seance, I think you really have to go for something like morbid and fill your deck with cards like Skirsdag High Priest and even Reaper from the Abyss. (If you're playing legacy, you might even throw in that pair of Diamond Valley(s) while you're at it.)
With something like the reaper, his morbid trigger will activate at the same time Seance would have exiled him. So if you somehow get him into your graveyard, cast a Seance, bring him back as a Spirit, and activate morbid (either on your turn with sac or on your opponent's turn as a blocker), you get to kill a free creature along with any other morbid shinanigans you have going on.