#8 Tuktuk the Explorer
Initially dismissed out-of-hand as a crap rare, and still dismissed by some, the sacrificial Goblin is more than meets the eye. The prevalence of Diabolic Edict effects ensures that you have both removal and a way to cash in Tuk Tuk for his big finish - a 5/5 colorless token. Many games in testing have gone on longer than necessary since his token means that Sejiri Steppe no longer makes their best attacker unblockable. While he might not be the next tournament superstar, this little guy gets more work done than he initially appears to. He's preselling for very little, so he is a high-upside low risk play.
#7 Consuming Vapors
While not as cheap as Tuk Tuk, Consuming Vapors is preselling for closer to $5. It has the potential to be a game-ending blowout and has great synergy with Abyssal Persecutor and Gatekeeper of Malakir. The potential to shatter a board position and swing a race is very high, and it allows you to play cards like Tuk Tuk, Sprouting Thrinax and Abyssal Persecutor at max value. While it may not double in price, I'd rather have a playset at the pre-release rather than not.
#6 Momentous Fall
Yes, this card is obviously good. No, you still have no idea how good it is. In a playtesting game with some new archetypes, Momentous Fall cashed in a Knight of the Reliquary at the end of an opponent's turn, completely ending my opponent's chance of racing me and drawing me a whopping nine cards. The ensuing re-buy on Vengevine ended the game promptly.
#5 Mul Daya Channelers
Early testing is never concrete, but it has shown this card to be versatile and powerful to the extreme. Using fetch lands and Knight of the Reliquary to get a reshuffle can often turn your board position around, and if a deck is constructed to get the most value out of Channelers, you will often find yourself hitting very, very hard. The lack of consistency is the only thing keeping this card from being a marquee rare.
#4 Renegade Doppelganger
This card was a lot scarier when I misread it as copying any creature that enters the battlefield. Regardless, the card is still very powerful for the 1U cost. It effectively gives you a hasted copy of every subsequent creature you cast, which is most certainly something decks like Mythic would consider. The fact that it does not block worth a damn is keeping it from being a tournament powerhouse, but it still merits more consideration than the dollar bin. Probably high risk, but also a possible high upside.
#3 Sphinx of Magosi
This is only on the list because it's criminally cheap. Yes, it's fighting against far better cards for the top spot in control decks, but by and large, untapping with this guy is bad news for your opponent. The ability to convert fallow mana into free cards is not to be underestimated, but since he dies to everything, care needs to be taken when playing this fattie. If it cost more than some spare change, it wouldn't be on the list, but since it's so cheap, it is a low risk, high upside play.
#2 Coralhelm Commander
There's an awful lot to like about this guy. The first thing to notice is his spot on the curve. A blue 2/2 for 2 is not something you'll write home about, but it is the first step towards being playable. The second most important facet is that he can hit level 2 on turn 3, at which point he becomes a 3/3 flier, and still allows you to leave up mana for Dispel or Spell Pierce. You can wait as long as you like to make him into a 4/4 flying Merfolk Lord, but it will only cost you 2 more mana to get there. At his ultimate, he's very, very good. I am imagining a Merfolk-based deck that abuses the 1-cost Counterspells in the format to protect its guys, along with Harm's Way, and locks out the game with Lullmage Mentor. The idea is untested, but the potential for this card is much, much higher than his $1.25 baseline preorder price would suggest.
#1 Vengevine
$25 is a lot, but after nay-saying this card, I put it in some decks. Card's real, people. Real, real good. It's quite easy to engineer situations to rebuy this beatstick without playing sub-par cards. Simply constructing one's deck to ensure Bloodbraid Elf always hits a creature ensures that Vengevine is an utter monster. Playing the card has felt colossally unfair, as unearthing two can often end the game on the spot. It has synergy with some of the best cards in Magic right now, and brings its A-Game against the field. It's great against most of the incumbent decks, notably Jund and UW Control. $25 might be the right price, but given the sheer power of this card in the games I've played with it, it might even be a little low. It doesn't have the appeal of a Planeswalker or a giant Angel, but expect Vengevine to be a defining card of Standard for the coming year.