Aaaand now you're thinking: this gal is completely unqualified to talk about awesome cover designers. You are, as usual, completely correct.
At my level of power in the biz (i.e., none), I don't talk to artists, designers, or art directors. I don't offer feedback on final designs. I don't get a yes or no. If there's something truly wrong about a final cover, I can point out that detail and it may or may not change. I think the reasoning here is that I don't know markets or reader expectations nearly as well as the people who are in charge of bringing my story to the public. So I bow to their experience and expertise.
However! What I can show you is a peek at the one thing I do get to contribute to the cover-design process: an information packet that describes the characters and setting. I send these in at product launch time, right at the beginning, and they are supposed to function as a cheat sheet so the designers and artists don't have to slog through reading the whole book.
I love filling out these things and sharing my inspirations and wishes; it's one of my favorite parts of book production. Here's what I sent Sourcebooks for Perfect Gravity (note that the images I included are all copyrighted, so I can't post them here, but I've included a short description of each in [brackets] and I'm sure your imagination or Google-fu can illuminate the rest):
| 
Hero (Kellen Hockley) | 
Race:  Texan
  (okay, not a race, but definitely a type) 
Complexion: Tan from spending a lot of time outside 
Age:  30 
Body (height/build): 
  He gets a lot of exercise. Um, I used this image for inspiration: 
[pic of Scott Eastwood shirtless] 
Hair color/length: dark blond 
Eye color (one word): 
  blue 
Facial hair?  Nothing
  really in the story, though he does go a few days without a shave there in
  the middle and could definitely be scruffy. 
Clothing: He wears jeans and boots a lot. Stetson
  sometimes (outdoors only, because down-home manners!). A belt buckle. At the
  very end of the book, at a fancy-dress shindig, he wears a tux. Thusly: 
[pic of Scott Eastwood in a tux] 
  Signature Accessory: A cat. He rarely goes anywhere without Yoink, a cloned,
  bionic kitty. She’s cinnamon-and-white striped and has metal horns protruding
  from her wee skull, near her ears. The details aren’t hugely important. If y’all
  decide to put a cat on the cover, I don’t think it matters too much what kitty
  looks like. 
[pic of shirtless cowboy holding a cat] 
My dream cover for this book would feature a
  shirtless cowboy holding a bionic cat. But probably that stock photo would be
  really, really hard to find. | 
| 
Heroine (Angela Neko) | 
Race:  Bengali/Japanese 
Complexion: more South-Indian than Japanese, so kind of
  latte 
Age:  early 30s 
Body (height/build): 
  short, slight, in command (of everything). Bit Napoleonish. 
Hair color/length: Black. Can be in any style: she goes
  from having a super fancy updo to being bald to having a short pixie cut at
  the end. 
Eye color: dark brown 
[pic of Priyanka Yoshikawa] 
Clothing: Conservative high-fashion futuristic chic.
  Tailored to within an inch of her life, but with flights of couture weird. In
  terms of style and deportment, I think of her as a mashup of Huma Abedin,
  Padme Amidala, and Alexander McQueen. 
[pic of Huma Abedin in her wedding dress] 
[pic of vaguely steampunk long-sleeved Alexander McQueen dress with buckles and frogging on the bodice] 
[pic of Padme Amidala in her heavy velvet addressing-the-Galactic-Senate costume] 
Key Accessory: Elbow-length biodeterrent smartgloves. (That, uh, just look
  like regular gloves, those heavy-duty long things the Victorians wore to keep
  the whole world off their skin.) | 
| 
Setting/description (similar to first book in series) | 
The year 2059, so near future. Look should be futuristic
  but gritty. 
Western U.S. desert (so, lots of scrub-brush flora and
  bumpy horizons) with an unexpected giant megastructure (an arcology, like
  those mongo buildings in BladeRunner) jutting out of a vast, dark nothing.  
Also
  scenes in post-apocalyptic underwater Galveston and a futuristic Guadalajara. | 
| 
Design ideas/inspiration | 
This movie poster sums up the mood nicely: 
[pic of Cowboys vs Aliens movie poster featuring Daniel Craig's backside] | 
| 
Cover descriptive words | 
Techno, sexy, old-west, bleak, futuristic | 
And this is the cover they came up with:
I think the cover is gorgeous. Does it match my vision? Not really. But it fits smoothly into that urban-fantasy kickass-heroine market, which is where I suspect the publisher was trying to place it.
So, yeah, it's probably best I don't have a lot of control over covers. There are people who are much better at this than I am.
But, just the tiniest bit, I do mourn the shirtless-cowboy-with-a-robot-cat cover that never was.

