Hokusai
Hopper
Bosch
Van Gogh
Albrecht Dürer
Ansel Adams
Brancusi
Moore
Rodin
Christo & Jeanne-Claude
Maurice Sendak
Chris Riddell: Chris Riddell - Wikipedia
Mark Ryden (already linked, I see) : http://www.markryden.com/paintings/index.html
Ursula Vernon : http://www.metalandmagic.com/
Al Hirschfeld’s the only name that comes to mind right now.
But if you have to ask why, you’ll never understand.
Mark Ryden (already linked to in this thread)
Trevor Brown (I really can’t link to his stuff because it’s NSFW, but it’s amazing. Search at your own risk)
Chris Ware - link to one of his building stories
Takashi Murakami (invented “superflat,” and iconic images like Mr. Dob and “My lonesome cowboy” (google image search that one when you’re not at work)
Kozyndan - husband and wife illustration/graphic design team. I have a signed and numbered print of this panorama of their hanging over my couch.
Mel Ramos - weird cheesecake/pinup art of women posing on gigantic cheeseburgers, with big ketchup bottles, and so on. Google it.
The Archigram Collective - sixties french conceptual architecture designs like the walking city.
Paul Laffoley, whose wall-sized paintings combined architectural designs, occult and alchemical schematics, and pure nutjobbery into amazing, HUGE, ridiculously complicated designs like the Thanaton III, which Laffoley thinks is actually alive, and the crazy Metatron angel thing.
Joe Coleman - quasi-NSFW, so google it, but Coleman does absolutely amazing, comically detailed biographical pictures that tell stories by showing the stories all around the main biographical subject. They’re really insane to look at for an extended period of time.
Bill Ward - hands-down the best pinup artist ever. Done. Inarguable.
Daniel Clowes - my favorite comic artist. I like the way that his stuff has evolved.
I think those are utterly bizarre, yet very strong and complete. I’d like to see them in person, see what they really feel like. They carry pretty well, even in tiny online images.
I had a much harder time with yanceylebeef’s Shag. Those images carry strong connotations for me, I remember design elements like those on my parents’ paperback books and album covers. I kept thinking I saw cigarettes.
What is this “don’t ask, can’t tell” stuff? I don’t understand. I wouldn’t expect you to convince me that I should like it, but I’d be interested in hearing why you do.
Euty, your Greg Stones reminds me a lot of Eric Fischl-- you might like.
Takashi Murakami is a riot. And Kandinsky (before he bought a protractor and compass) and Gerhard Richter rock.
That stuff’s totally awesome. I had never heard of it.
Someone mentioned Hokusai, and you can’t do that without also mentioning Hiroshige. 
As someone who started out as an Illustration major, I have a special place in my heart for Art Noveau; so, I bring you Mucha and Harry Clarke.
And, as someone who is now a Comics major, I have a special place in my heart for William Hogarth’s serial storytelling paintings, in particular, Marriage à-la-mode and Windsor McCay’s Art Noveau-styled comic Little Nemo (I’m sorry I can’t find a good gallery of this online. They had a collection at the Newark Museum a few months ago, as part of the Masters of American Comics show. The originals are enormous and gorgeously inked and colored. If it’s still up, I highly reccomend anyone in the Jersey area to check them out. Also part of the collection were Dick Tracy, Peanuts, Terry and the Pirates, Krazy Kat, and Gasoline Alley).
For something a bit more contemporary:
Yan Nascimbene.
Also, Takato Yamamoto, whose pictures I cannot link because they’re NSFW. Google for his name; the first two links have small sections of his stuff. It’s mostly semi-nude beautiful young men or women in detailed, morbidly decorated environments in style that he developed based on Ukiyo-e (which is the style of Japanese woodprints Hokusai and Hiroshige did. Edo period stuff.)
I like his colors and his use of light. Some of the compositions didn’t feel quite right, but others were effective.
I’ll bite. Why can’t you share your reasons?