Ok, let's start with a premise: black devotion decks are better than their red counterparts in Standard. Examine the reasoning behind that premise: Whip of Erebos and Rescue from the Underworld to recur it's enter the battlefield effects, unconditional removal in Hero's Downfall to go along with Doom Blade, access to life gain thanks to its Gray Merchant of Asphodel.
Red can recur Chandra's Phoenix and try to generate value through Young Pyromancer, rely on Magma Jet and Lightning Strike for removal and some deck manipulation but gaining life is a problem. When your opponent gains life, red has always had a difficult mountain to climb, but red decks not gaining life themselves means blue's turn three Nightveil into turn four Master of Waves is too difficult to recover from. Against blue aggro, red's best solution is Anger of the Gods. That card is too symmetrical for Red to rely on it to steal a victory.
So what? You are here to make money. Well, correctly judging a deck's/card's playability is the easiest way to trade, buy and sell profitably. To evaluate cards and ignore the environment they are most likely to be played in (Standard) is a mistake. Scrylands are terrible, right? I mean, sure they are better than a dead land draw late, but when Shocklands offer speed and flexibility it isn't too surprising these newer dual lands have a hard time appreciating in value.
Of course, when Shocklands rotate players will be left with ONLY Scrylands. Smell the opportunity? You don't need a smart phone to pick up out of favor cards for your "good stuff". I know most QS readers have loaded up on Shocklands. They remain an excellent pick up, but trading into two or three of the Scrylands for a single Shockland will hedge your position. Shocks leaving Standard will have a negative impact on their pricing, at least temporarily, but the positive effects that rotation will have on Scrylands will help you weather the post-rotation price flux.
I've had several players complain in my company about Purphoros and his progressively worsening value. Well, consider the opening paragraph of this article and you have a reasonable explanation for the red god's decreasing popularity. Meanwhile, Whip of Erebos is a three dollar card that can function as an engine/ finisher in black devotion decks. I already like the Whip to get to $5 thank's to it's casual appeal (Commander), but reanimation is always a popular strategy and this is one of its few enablers in Standard.
Master of Waves was totally under appreciated. A merfolk always deserves extra attention thanks to the Legacy archetype. The Master looks pretty good in decks that are likely to have 4-5 devotion when he lands. In standard, he might expect 3-4 devotion when cast. That means 4 mana for 4-5 permanents. That is card advantage better than Opportunity at -2cc.
Seems more than a little playable in Standard, but people still doubted the card because "it dies to removal." Theros gave us more counterspells and Negate is still in the core set. The profitable trade is behind us now, but it's always worth examining the "why" behind card spikes. While supply constraints lead to plenty of unpredictable spikes in formats with a larger card pool, a spike in Standard is more often evidence of the ignorance of crowds. If you love value, knowing you can always count on others to misjudge cards is great news.
Devour Flesh has a place to shine in standard, and always looked like a common powerful enough to compete for space in every MtG format. If you can still pick this up as a throw-in or as if they were "just another" common go ahead and start squirreling them away next to your collection of Dark Ascension's Tragic Slip. This thing is worth at least twenty five cents, no? You can likely trade out to Standard players in need for at least that much today, and if not ending up with many copies of any playable Magic card is a winning proposition.
Thoughtseize is sporting some new art! Apparently that means it's now worth a lot less. Here is a card that will be run as a four of in Standard decks for months to come, that's also already proven itself in older formats. I know plenty of Theros is being opened, but picking these up with the modest expectation they get to $25 seems like a pretty safe assumption. If you doubt that, at least spend some time looking at the price of Scavenging Ooze over the last 3 months.
Just in case you aren't paying attention, or can't read between the lines: I like the Scrylands at these sub $5 prices. I'm looking for them to reach $10 once players in Standard have fewer options. Whip of Erebos looks cheap too ($3), it contributes mightily to consistency in Standard decks that run it and has a lot of casual appeal. Thoughtseize is suffering a price move in our direction, lets take advantage of easy plays when we can. Along the lines of Devour Flesh: I know most of us see the value in Young Pyromancer and pick them up cheaply whenever possible. Did you know that Guttersnipe is still worth at least half as much to dealers? When you are in a room full of people obsessing over value, make the easy play for the cards they ignore/devalue.