Children's book series before Harry Potter
The Three Investigators were akin to the Hardy Boys, I guess, but I preferred the Investigators. The author of the first 10 books or so was Robert Arthur, though by the time new authors took over, I had mostly outgrown them.
Preparatory to writing that post, I was curious to see if the books were still available, or even listed, on Amazon.com. It turns out that though the original books were published in the 1960s and '70s, they were reprinted in the 1990s, with Alfred Hitchcock written out for some reason (probably having to do with licensing, i.e. money). Even those reprints now appear to be only available secondhand. That's a shame.
The Three Investigators weren't rich and they weren't "cool." Their leader, Jupiter Jones, was brainy but "stocky." Kind of like a 13-year-old Nero Wolfe. One of the other members had recently had a leg brace removed, so he wasn't exactly athletic either. They worked from a hidden clubhouse in Jupiter's uncle's junk yard. Some of their cases seemed to have a supernatural component, which was always debunked by the end of the story ("The Secret of Terror Castle" turned out to revolve around a Lon Chaney type actor ~ the "Man of a Million Faces," as opposed to Chaney's Man of a Thousand Faces ~ whose career had been ruined by the talkies) or a puzzle ("The Mystery of the Stuttering Parrot" featured a parrot that said "To-to-to be or not to-to-to be, that is the question," which raised the REAL question of why would someone teach a parrot to stutter Shakespeare).
If you're curious, try a library or used book store, and try to find the original versions if you can.
Did you have a favorite series as a child? Have you checked to see if it's still in print? Let me know.