Kaladesh is an exciting set, and the new Standard is pretty interesting. My pick for the sleeper of the new set is Scrapheap Scrounger, reminds me of Hangarback Walker and Gravecrawler. I can see these at an easy $5 short-term, but this has the potential to break out in a big way, as it's playable in lots of decks, has strong Standard synergies which are not extremely obvious, and moreover no one likes to admit that a 3/2 bruiser over the head on repeat is the state of the art in Magic. That said, Star City games is sold out.
Crush of Tentacles is surging upwards in price for a second time in Standard (a sure sign of a strong card). This seems really, really good. Evacuation gets some play in Modern, right? This is arguably much better. I like the idea of using a Distortion Strike on your own biggest threat, attacking, then Surging the Crush of Tentacles, giving you the 8/8 Octopus on an empty board, and a rebounded Distortion Strike the next turn for an unblockable 9/8 Octopus. That's fourth or fifth turn in Modern. This card looks so Timmy, so clunky and non-competitive, which is why (I think) it's gone under most radars.
And, finally, Collective Brutality. I think this will go the way of Kalaghan's Command (headed to $12+ in the near-term). So versatile, so many syngeries, so cheap.