[Crimsy]

What a great resource you have here. I discovered it after Larsen mentioned it in SD.

I'm trying to get a feel for comics from the '40s and '50s, to better understand what those eras of comic history felt like. I'd appreciate your opinion on which comics and creators best represented those two eras similar to how, say, Kirby, Ditko, and the early Marvel books represented the '60s as far as mainstream comics.

I have Marvel Unlimited, so there is no need to limit answers to comics found on this site.

[paw broon]

Wow, there's a lot in your question.  Thank you.  Most interesting. 
However, it's a very American centric question.  Other countries have an amazing depth of comics history with work that easily equals that of the American comic.  I hope lots of you pile in with suggestions but Crimsy, you'd be doing yourself a disservice if you don't check out the work of creators in Spanish, French, Italian, Dutch, Belgian, British and I suppose Japanese comics.  Australia had its own comics industry before the arrival of American comics in the country.  So if you have the time or inclination, please check the other sections on the site.  You'll find some excellent stuff.  But of course there's so much more we can't host for copyright reasons, but it is out there on many sites to be discovered.
As for American titles and creators from those decades, the obvious ones, to me at least, are certainly Will Eisner and The Spirit, Jack Cole and the wonderful Plastic Man, Mac Raboy's graceful interpretation of Cap. Marvel Jr., the almost beautiful work of Lou Fine on The Ray and The Black Condor.  One of my favourites is The Black Terror and as for art, the issues with Jerry Robinson and Mort Meskin at the helm are nice stuff even if the Terror has been de-powered.  I have a liking for the early Captain America stories by Simon and Kirby, and they are very important in the history of comics, even if Cap wasn't the first "flag" hero.
Some newspaper strips are worth mentioning and the stories were reprinted in comics. First, Rip Kirby by Alex Raymond - quite superb.  Ray Moore's work on The Phantom is most enjoyable. 
I'll let others weigh in.

[Electricmastro]

Jack Alderman is one Id like to point out. His art style reminds me old 40s film noir movies with an emphasis on shadow, menacing feelings, and a style resembling movie posters. His faces can be seen as a downside, though they might still serve as a support to the overall uneasy his art tends to give off, particularly with crime comics.

Captain Aero Comics #11 (September, 1943):



Cat-Man Comics #22 (December, 1943):



Crime Does Not Pay #49 (January, 1947):

[The Australian Panther]

Hi Crimsy, [From Crimson? Or crime? or the German, Krimi?]

I'm trying to get a feel for comics from the '40s and '50s, to better understand what those eras of comic history felt like.

A great quest to embark on!

I'd appreciate your opinion on which comics and creators best represented those two eras similar to how, say, Kirby, Ditko, and the early Marvel books represented the '60s as far as mainstream comics.

Well, before Marvel reduced the US action comic output to comics done by the Marvel Method, there was much more variety in US comics. And to really get the picture you need to go back to comic strips, Action strips like Tarzan, Dick Tracy, Flash Gordon, to name only a few of the better known ones, had huge audiences before comic 'books' existed. Then there were the 'Pulp' magazines which introduced characters like the Shadow, Doc Savage and the Spider. And the science fiction magazines which introduced characters like 'the Lens-men' which were the inspiration for the 60's Green Lantern.

My suggestion, if you want to learn, look at the threads on this site, find one that interests you and then go to the comics discussed in those threads.
Start with the 'comic talk' threads, here.
https://comicbookplus.com/forum/?board=8.0

Also, bear in mind that CB+ posts books that is PD, - in the public domain - and a lot of comics are not in the public domain.
In the Golden Age, EC comics were very important and influential.
There are no DC or Early Marvel [Atlas and Timely] comics on this site.
Also nothing from King Features [Tarzan, Phantom,, Flash Gordon, Prince Valiant, Mandrake and others - all of which are important in comic history]

Jack Kirby was influential way before Marvel, and you will find much of his work here. Have a look at his romance comics as well. Also you will find Ditko here. If you know the 60's and 70's artists from Marvel and DC, you will find earlier work here from most of them. But there are many others here just as good.

Also, check out the threads in the Comic Book Plus Reading Group where we discuss individual comics in detail. And please join in.
https://comicbookplus.com/forum/?board=26.0

When it comes to looking at our Non-English books, don't worry if you don't speak the language, Comic books are primarily a visual medium and many of the stories are generic, so you can often work out the basics. But there are some great artists there.
In the English speaking section, you will find comics from the UK, Australia, New Zealand, Canada and South Africa.     
Crimsy, if you are jut beginning this adventure, I envy you! You have just fallen down the rabbit hole!

Cheers!