1. The first category to look at is the most obvious one: spend X mana to cast a card, and when it enters the battlefield, you get Y energy.
2. The second category, mostly for creatures, involves earning an ETB Energy and spending it on that creature or another creature.
3. The third category is a catch-all for various other ways to earn Energy or to spend it.
Glassblower's Puzzleknot: [Category 1] 2 mana in, 2 Energy out, then 3 mana in, 2 Energy out. Each time you can Scry 2.
Woodweaver's Puzzleknot: [Category 1] 2 mana in, 3 Energy out, then 3 mana in, 3 Energy out. Each time you have a 3 life bonus.
Decoction Module: [Category 3] 1 Energy for every creature that enters the battlefield. Then you can spend 4 mana to send a creature back to its owner's hand, and that can mean you if you want to bounce something and get another ETB bonus.
Fabrication Module: [Category 3] This is the other half of the equation that was set up in Decoction Module. With this artifact you can recycle Energy to +1/+1 counters. This artifact is very useful.
Animation Module: [Category 3] Easily one of the best engines in the Energy economy. You can take the counters you got from Fabrication Module, or from one of the triggered conversion of Energy to +1/+1 counters, add a one mana, and come out with a 1/1 artifact creature token. For three mana you can add a counter, any counter.... this seems really strong.
Demon of Dark Schemes: [Category 3] Another creature dies, and you get one energy. That's not much of a bonus unless your whole deck profits from destroying your own creatures. The reanimation clause is the one that I think really matters. 3 mana and 4 Energy to reanimate any creature. I would reanimate something really menacing, and so would you.
Aetherworld Marvel: [Category 3] There are many ways to put a permanent into your graveyard, and it does not have to be a creature. That can be a really cheap way to earn one Energy per permanent. That six Energy will need to come from somewhere else for this artifact to be as strong as Quicksilver Amulet (4 drop, Pay 4, Tap: You may put a creature card from your hand onto the battlefield).
Consul's Shieldguard: [Category 2] ETB yield is 2 Energy for 4 mana, then you can spend 1 Energy on an attack trigger to make another creature Indestructible.
Aetherstorm Roc: [Category 3] One Energy for every creature entering the battlefield can be a lot of Energy, except this is 4 drop. You would have to be casting a lot of small creatures turn 5, and play against control for many more turns and not get your creatures countered... This card does not seem like a great Energy engine.
Thriving Ibex: [Category 2] ETB yield is 2 Energy for 4 mana. The attack can get a +1/+1 counter for 1 Energy.
Eddytrail Hawk: [Category 2] ETB yield is 2 Energy for 2 mana, then you can spend 1 Energy on an attack trigger to give another creature Flying.
Aether Theorist: [Category 2] ETB yield is 3 Energy for 2 mana, then you can spend 1 Energy to Scry 1.
Janjeer Sentry: [Category 2] ETB yield is 2 Energy for 3 mana, then you can spend 2 Energy to tap or untap a creature or artifact. The artifact bit is VERY important, as in you get to have a Voltaic Key (1 drop Artifact, Pay 1, Tap: Untap target artifact.)
Minister of Inquiries: [Category 2] ETB yield is 2 Energy for 1 mana, then you can spend 1 Energy to mill for three.
Aethersquall Ancient: [Category 3] ETB yield is 3 Energy for 7 mana, then you can spend 8 Energy to return all other creatures to hand. It's a late effect, but it's a really good one. It can be pulled off in Constructed in a strong control shell and I am sure it's a really awesome move in Commander.
Hightide Hermit: [Category 2] ETB yield is 4 Energy for 5 mana, then you can spend 2 Energy to undo the Defender limitation.
Thriving Turtle: [Category 2] ETB yield is 2 Energy for 1 mana, then you can spend 2 Energy for a counter.
Whirler Virtuoso: [Category 2] ETB yield is 3 Energy for 3 mana, then you can spend 3 Energy to drop a 1/1 token.
Empyreal Voyager: [Category 3] Deal combat damage to a player for 1 Energy. Flying will often be enough if your opponent does not have any flyers. And if not, even Trample sometimes will let you satisfy the condition and get you that Energy.
Voltaic Brawler: [Category 2] ETB yield is 2 Energy for 2 mana, then you can spend 1 Energy for a one time +1/+ boost. The one time clause seems weak, but you are playing a 2 drop 3/2 at uncommon, and that is an aggressively costed creature.
Thriving Rats: [Category 2] ETB yield is 2 Energy for 2 mana, then you can spend 2 Energy on a counter.
Thriving Grubs: [Category 2] ETB yield is 2 Energy for 2 mana, then you can spend 2 Energy for a +1/+1 counter.
Territorial Gorger: [Category 3] You can spend 1 Energy to one time boost this creature for +2/+2. That's a solid boost and a great way to funnel a lot of Energy in one hit in the correct situation.
Spontaneous Artist: [Category 2] ETB yield is 1 Energy for 4 mana, then you can spend 1 Energy to give a creature Haste. This is a great effect that only rarely works. It's too much setting up most of the time.
Aethertorch Renegade: [Category 2] ETB yield is 4 Energy for 3 mana, then you can spend 2 Energy to deal 1 damage to target creature. And then you have an additional clause, and you can spend 8 Energy to smack face for 6. That clause will be rarely used, but when it is, it can win you the game, especially in Limited.
Maulfist Doorbuster: [Category 2] ETB yield is 2 Energy for 4 mana, then you can spend 1 Energy to cause a creature not to block. That's useful often.
Lathnu Hellion: [Category 2] ETB yield is 2 Energy for 3 mana, then you can sacrifice it 2 more Energy.
Servant of the Conduit: [Category 2] ETB yield is 2 Energy for 2 mana, then you can spend 1 Energy to get one mana of any color.
Architect of the Untamed: [Category 3] ETB yield is 1 Energy for every land ETB. That's really good. This thing is an Energy engine. You can also pay 8 and drop a 6/6 token. I see the token clause working often if you have ways to protect this creature.
Sage of Shaila's Claim: [Category 1] ETB yield is 3 Energy for 2 mana, then you can spend the Energy any way you want. This is a great card in the Energy economy.
Bristling Hydra: [Category 2] ETB yield is 3 Energy for 4 mana, then you can spend 3 Energy to place a +1/+1 on this creature and give it end of turn Hexproof.
Thriving Rhino: [Category 2] ETB yield is 2 Energy for 3 mana, then you can spend 2 Energy for a +1/+1 counter.
Riparian Tiger: [Category 2] ETB yield is 2 Energy for 2 mana, then you can spend 1 Energy to
Longtusk Cub: [Category 3] ETB yield is 2 Energy each time this deals combat damage to a player. Since it doesn't have Flying or Trample, the Energy-earning condition may not end up taking place that often.
Electrostatic Pummeler: [Category 2] ETB yield is 3 Energy for 3 mana, then you can spend 3 Energy to give it +1/+1 counters for each power. That means you need to come up with a way to boost this, otherwise all you will get is a +1/+1 counter for 3 Energy. There are many ways to make a creature big in Modern, and there the 3 Energy can yield many more +1/+1 counters.
Multiform Wonder: [Category 3] ETB yield is 3 Energy for 5 mana, then you can spend 1 Energy in two ways: give it Flying, Vigilance, or Lifelink; or make it a 5/1 or a 1/5.
Consulate Surveillance: [Category 2] ETB yield is 4 Energy for 4 mana, then you can spend 2 Energy to prevent damage. This is usually a lame effect except in a focused Fog deck.
Confiscation Coup: [Category 3] ETB yield is 4 Energy for 5 mana, then you can spend Energy to gain control of an artifact or a creature. This effect is in a long line of 'take control' cards.
Live Fast: [Category 3] ETB yield is 2 Energy for 3 mana, then you draw two cards and gain 2 life. It reads like this Standard's Read the Bones.
Harnessed Lighting: [Category 3] ETB yield is 3 Energy for 2 mana, then you can spend 1 Energy for each 1 life hit to a creature. If you could also deal that damage to a player, this card would have been much more playable.
Attune with Aether: [Category 3] ETB yield is 2 Energy for 1 mana, then you get a basic land from your deck.
Dynavolt Tower: [Category 2] ETB yield is 2 Energy for 3 mana, then you can spend 5 Energy for a Lightning Bolt effect (three damage to target creature or player)
Deadlock Trap: [Category 2] ETB yield is 2 Energy for 3 mana, then you can spend 1 Energy to tap and mute activated abilities. If you can use this to freeze a planeswalker, that's pretty good.
With 43 cards in the Energy economy, there is plenty to do out of this one set.
