Pulp Madness!
Finishing off Pulp week here at Monster Brains, here is a gigantic gallery of sci fi and fantasy pulp covers spanning many decades and dozens of publications. The number of covers they have collected here is really impressive, there must be at least a couple thousand pics to browse through. They have sections for pulp magazines, paperbacks, interior illustrations, and many French language magazine covers.
The section where I found some of the most interesting and strange art was under the cover section for the magazine "Fiction". Check it out.
Check out some of these really weird covers. 1 2 3 4 5 6 7

Vintage Octopus Pulp Covers!

More Sci Fi and Horror Comic Covers
This first link has a collection of "classic crime and horror covers", with an array of horrific scenes of monsters, aliens, zombie freaks and other weirdos.

This gallery hosts the covers of Weird Fantasy, Weird Science Fantasy and Weird Science by E.C Comics.

The Timely Atlas Cover Gallery has a selection of 361 horror covers with titles such as Amazing Mysteries, Spellbound, Journey Into Unknown Worlds and many others.

Disobey.com has a gallery dedicated to many horror covers. They've got a section for E.C horror covers as well as various other horror comic covers.

The "Groovy Age Of Horror" blog has many great articles on pulp horror of the past decades. This post concerning a severed hand is both disturbing and hillarious.

And I can't make a post like this without mentioning Hyper Dave and his datajunkie blog. I'm sure many of you are already aware of this place but for those who aren't, start here and work your way up. There is a vast collection of sci fi and horror comics with large scans of covers as well as entire issues to be downloaded here, not to mention old radio programs and many other interesting things fitting into this genre.

Monster Magazine Covers
Here is an incredible collection of pulp magazine covers of the horror variety. From Creepy, Eerie, Tales From The Tomb, Nightmare, and many other titles, there is a great selection of horrific and fantastic covers to check out here.

Fletcher Hanks
Fletcher Hanks comics are filled with rigidly drawn characters battling bizarre forces with powers that are both Godlike and surreal. The use of primary colors in most of Fletcher's comics only adds to the strange dreamlike atmosphere of the stories.
Scroll to the bottom of the link posted above to see 3 Fletcher comics. Below you'll find links to various Fletcher Hanks comics. Unfortunately there's pop ups in a few of them, so beware.
Stardust The Super Wizard from Fantastic Comics #1
Stardust Vs The Emerald Men
Stardust in Fantastic Comics #6
1 2 3 4 5 6
Stardust The Super Wizard from Fantastic Comics #13
Stardust in Fantastic Comics #14
1 2 3 4 5 6 7 8
Stardust in Fantastic Comics #16
1 2 3 4 5 6 7 8

Fantomah
Another Fantomah Comic
More Fantomah

Thanks to Rob Lashaw for many of the links.

Virgil Finlay
Another great artist associated with pulp comics, Finlay's intricate linework is comparable to the likes of Gustave Dore or Albrecht Durer. 

See Datajunkie's posts showcasing scans of Finlay's art by click the following numbers... 1 2 3

Click here to see an illustration Finlay did of a Lovecraft story, part of which can be seen above.

War Of The Worlds
Carrying on with the pulp art, here's a great collection of artwork related to the H.G Wells story "War Of The Worlds".

Frank R Paul
2nd Gallery - Scroll through the pages below to see additional work.
3rd Gallery
4th Gallery
Many high quality copies of Paul's black and white illustrations have been posted over at Datajunkie.
You can find more artwork by Frank R Paul along with other pulp artists at this gallery.

Thanks to Hyperdave at Datajunkie for bringing this artist to my attention.