Mark Rosewater left us with his customary set of teasers on his Monday column: http://www.wizards.com/default.asp?x=mtgcom/daily/mr296
Here are the teasers:
- the next evolution of a popular cycle from Mirage
- a 10/2 creature for

(okay, there might be another cost) - a green enchantment that can keep the 10/2 from hurting you
- a cycle of creatures that lets you use a resource first seen in Unglued
- a card that makes all your Treefolk indestructible (I know you already know it; it's still cool)
- a white answer for any bothersome nonland permanent
- a Shapeshifter lord
- an artifact that lets you play spells for free
- lands that provide two colors of mana and can come into play untapped
- and a card that finally cares about Goats
I'm going to pull out a few of these for speculation.
1) "the next evolution of a popular cycle from Mirage" The first mirage cycle that springs to mind is the oft imitated "Charm" cycle. While this is always a possibility we've seen charms pretty recently (in TSB and PLC sets). Given the nature of this set as a tribal block my wild guess is that we'll see something along the lines of the "Spirit of the Night" cycle - creatures that can Voltron into something larger.
2) "a green enchantment that can keep the 10/2 from hurting you" Barbed foliage was one of my favorite cards in Mirage block - especially sealed. Perhaps we could see a more focused iteration? Doing two damage to one attacking creature rather than one to all attackers? Alternatively it may prevent attacks completely from some sources a la moat. A reverse moat (fliers may not attack) would certainly be in keeping with the reach mechanic the green is famed for.
3) "lands that provide two colors of mana and can come into play untapped" So the question is: which of the Future Sight dual cycles will make its full appearance in Lorwyn? Grove of the burnwillows and River of Tears" seem to be the prime candidates to me based on flavor text. River of Tears was my gut choice but the flavor seems like it might be more in line with the next mini-block than Lorwyn, still I'm going with the River. Interestingly assuming one of the FUT cycles is expanded that means one color combination is short a dual land in standard.
4) "a cycle of creatures that lets you use a resource first seen in Unglued" I bring this up for brainstorming help because I wracked my brain an couldn't think of what Rosewater could be referring to. But then I was relying on wikipedia and gatherer searchses to try and tract down this clue as I've held all of one unglued card in my life. The term "resource" is odd enough that I don't think it is something as simple as more "enchant player" cards (that debuted in unglued and were subsequently printed in TSP and FUT).