Magic Traders added Zendikar to its pricelists yesterday, which means the data is flowing into BLP. Lotus Cobra is not surprisingly the highest valued card at the moment ringing in at nearly $25! We'll see in the coming weeks whether it truly can hold that high price tag.
Zendikar only has three entries in the top 15 highest sellers at the moment: Arid Mesa, Misty Rainforest, and Goblin Guide. However, that should slowly change as product makes it into more players' hands.