(From a comment made in an earlier post, which I think merits a post of its own)
If you’re looking to jump into reading Pulp, here are some suggestions:
First up, an excellent overview, which might give you an idea of what directions you’d like to look toward:
The Great Pulp Heroes by Don Hutchison. It’s probably the best overview I’ve read to date, organized by chapters devoted to the big name characters and magazines.
Nostalgia Ventures has been doing two-novels-per-issue reprints of the original Shadow and Doc Savage pulps, complete with original interior illustrations, and historical commentary by Will Murray. Well worth your time.
There have also been reprints of The Spider, by various publishers, easily found by searching on Amazon under “The Spider”, “Grant Stockbridge” or “Norvell Page”.
Baen recently produced The Spider – Robot Titans of Gotham, which reprints two complete Spider stories, and is a good introduction to the character.
From there, doing searches on characters — “Operator #5”, “Secret Agent X”, “Phantom Detective”, etc. — will lead you to various reprints that are available.