My top three five picks:
Chris Goodwin can illustrate like a powerhouse, and comes packed with so many various styles in his repertoire that he can practically be ten artists in one. Plus, he’s been a professional illustrator for quite a few books before, most notably Ironclaw/Jadeclaw. https://www.furaffinity.net/user/chrisgoodwin/
Kamui’s work begs to be found on a book, or many a book, and posters. He’s got talent on par with Goodwin and his own deft, dramatic realism to his style. https://www.furaffinity.net/gallery/kamui/
PseudoManitou’s work follows in my tastes for Goodwin and Kamui’s work, and adds its own psychedelia and poster style. If you needed something visually striking, this is it right here. https://www.furaffinity.net/gallery/pseudomanitou/
BubbleWolf has a digital painting style that just screamingly begs to be put on the covers of novels. The painting style strongly reminds me of TOR and Baen books back in the 90’s, back when cover art was everything. https://www.furaffinity.net/user/bubblewolf/
Ryan Wardlow’s work is striking and distinctive, and probably another great choice for novels: https://www.furaffinity.net/gallery/ryanwardlow/
Honorable mentions:
Arphalia has a style I’d probably want to choose more for interior artwork than cover art, as her monochromes with ink tend to really shine, but she’s got all kinds of quality. https://www.furaffinity.net/gallery/arphalia/
Balaa doesn’t dip into the style often, but there’s times her full-colour paintings really look like they’d make a fine book cover. Example here: https://www.furaffinity.net/view/5516202/
There’s Blotch, of course.
Dramamine is currently doing the eye-poppingly wonderful “Night Physics” series which might make for a wonderful styling for furry psychedelia. https://www.furaffinity.net/gallery/dramamine/
Echin is another choice for someone I wouldn’t mind doing internal art for a book, especially his monochrome work. His work tends towards the hyper muscularized, though, so it limits his usability and appeal. Damn shame; he renders subtle expressions with tremendous finesse. https://www.furaffinity.net/view/10750640/
FaberCastel has an art style that invites itself to the covers of books, with the warm pastel hues and stylings. Example here: https://www.furaffinity.net/view/4200824/
Inku does elaborate, beautiful anthropomorphic psychedelia. Where Dramamine mines the drug-psychdelia, Inku’s on the other side of that spectrum, with fantastical whorls and patterns and symmetries and… oh, just go look. https://www.furaffinity.net/gallery/inku/
Kaji has some spectacular, spectacular paintings going on, poster art out the wazoo here. https://www.furaffinity.net/gallery/kaji/
Louvelex (https://www.furaffinity.net/gallery/louvelex/) would be my top choice for illustrating a children’s book. I mean, come on. This little burro playing a squeezebox is so cute it’s cheating! https://www.furaffinity.net/view/11157197/
NightRhino (author of the spectacularly illustrated ‘Carnal!’ graphic novels) has some gorgeous stuff happening, if you like your anthros gritty and scary: https://www.furaffinity.net/gallery/nightrhino/
Oouna’s done some work for me before, and I’d be remiss if I didn’t include her in this list: https://www.furaffinity.net/scraps/oouna/
Pac is currently doing a lot of the awesome stuff for the Furry Basketball Association project. https://www.furaffinity.net/gallery/pac/
RaccoonWolf’s rough painting style remains incredibly evocative, especially at full size/resolution: https://www.furaffinity.net/gallery/racoonwolf/