The rumors have begun it seems, according to 'Dewman' on MTGSalvation who saw a poster at this local store, we get the following tidbits for the upcoming set.

Three cards pictured on the poster are speculated to be the Release promo, and the 2 faction-specific Prerelease promos. Glissa would be the Phyrexian faction promo.

Thopter Assembly

Rare

Artifact Creature - Thopter

At the beginning of your upkeep, if you control no other Thopters, return Thopter Factory to your hand and put five 1/1 colorless Thopter artifact creature tokens with flying onto the battlefield.

5/5

140/155

MTGSalvation 12/23

Glissa, the Traitor

Mythic

Legendary Creature - Zombie Elf

First strike, deathtouch

Whenever a creature an opponent controls is put into the graveyard from the battlefield, you may return target artifact from your graveyard to your hand.

3/3

?/155

MTGSalvation 12/23

Also, Battle Cry is a new ability. According to CaptainBlack, it is an attack trigger. Speculation would put it on the Mirrodin side of the factions, if it is faction-specific.