This is why it’s so interesting. @comaestro says Paladins, Lowlands, and Raiders of the North Sea aren’t worker placement, but Beyond the Sun is. @yashima says Beyond the Sun is not worker placement but Architects is. @SteveB_uk says Architects is the best sort.
Of course, no one’s wrong. It’s just interesting how the lines can fall differently in these continuous spectrums.
I just go back to, the actual mechanics are action drafting, action point allocation, auction, area control, etc, and placing a token is an effective and flexible game state tracker that ends up linking these otherwise disparate things 
My own favorite examples of worker placement:
Agricola: I have to thank @lalunaverde for articulating this a while back. The problem with Viticulture, and many other WP games, is that there is one right path, and one best way to pursue it. Within this paradigm, classic WP doesn’t play well. Denial is harsh and leaves people pursuing something suboptimal. Which is why designers cheapen it with grandes or campfires or secondary placement spots. The genius of Agricola is how it pairs pure WP denial with point salad. Not only is everything worth doing, but the game enforces it. The first of anything is 2 points (first cow moves from -1 to +1) while incremental cows, or anything, are worth just 1/2 or 1. Also, each category is capped, you don’t score for more than 4 vegetables - again forcing you to diversify. This folds into WP so nicely because when you are denied, there is by definition something else worth doing. Wood gone? Forget animals, we’re plowing. You plowed? Well, I need to play this occupation eventually, I’ll do it now.
Agricola is a GPS that is constantly droning “recalculating…” and it’s craft is that there is always another route. Once I learned that, it wasn’t stressful any more.
Waterdeep: Another pure wp entry. I think I just talked about this, but the transparent math of the game (4 coins = 2 orange = 1 white, etc) and the fixed turns put the equation of how many, and which, quests you can complete right at your fingertips. Which means the horsetrading of how much this quest’s reward can accelerate you, or how much your opponent’s placement costs you, is also at your fingertips. And that makes it exciting. Corruption and new buildings, which accelerate the math with a cost, and the Undermountain cards, which take Waterdeep’s bare-bones mechanics and keep turning them in interesting directions, just make it better.
Raiders of the North Sea: I don’t like this game. But the put one / take one mechanic, along with the three levels of workers, is really smart. I love the shifting options and also the new way it makes players interact, combining denial with opportunity. Take that good action but now you’ve made a gold worker available… I’d love to see more of this with a better game on top of it.
Gugong would not be worker placement (it’s card placement, completely different…) but it’s similar. Each card you place has the location action, the card action, what opportunity are you making or taking from the table, what card are you picking up for next round… so it’s a bit like Raiders insofar as there are a half-dozen strings attached to each placement.
Bruxelles / Federation / Formosa Tea: These games use positioning of workers, in addition to action spots, in interesting ways. Bruxelles has your actions but workers are also engaged in various levels of area control. Federation has double-sided workers in addition to the area control, so you take your action but pair it with different auxiliary actions. Formosa Tea has field workers advance workers in another area - both your and others’ - which is this great shared incentive (or obstruction). Plus, if you advance your tea master to the end of its tea track you can take an action by picking it up, thereby extending your round with an extra worker. Beautiful.
Paladins of the West Kingdom: I like this for the action-point style of worker placement. Things are expensive, and you have to track color mix. So there isn’t competition over placement spots but it gives you a great puzzle in your own area. Pair that with the ability to invest in discounts and tailor your engine through the game with kickbacks or lower action-point costs, and it’s just satisfying.
Carson City: Probably my favorite of the fighty placement games. I like that, if you lose a fight, you get your worker back. Obviously, you wanted the space it was fighting over, but it’s nice that losing a fight puts you in a stronger position for the next fight or the next round.