If you happen to know or suspect what any of the unnamed books in this post are or who they're by, I would love to know.
The Hardy Boys. I read far too many of these, along with some Nancy Drew and Tom Swift, before realizing a deadly secret: they're all the same.
Pineapple Place. I remember little about this other than the name. When I checked recently, only the sequel was still in the library system.
Those Morgana books. I don't remember the title or author, but some children stumble upon a house full of mirrors. When a spell involving moonlight is worked, the mirrors became portals to another world, with the nice touch that on the other side you would appear however your reflection did here. Magic, originally contained in gemstones (if I recall), had been divided up into staffs of different ranks. There was a nasty game of questions in a dark basement. Someone is killed by shattering a mirror as he was passing through it. And one of the girls becomes Morgana's apprentice.
These books were really quite dark. I suspect I stopped reading them more or less intentionally, which is probably why I can't find them again now. Do I really want to? (This was probably somewhere between 3rd and 5th grade.)
Goosebumps. I also consider this wasted time now, although I suppose I know I don't like horror. I had a friend in second grade who had practically all of them and lent them to me.
Asimov, Norby and sequels. Who can forget this cute barrel shaped robot, hyperspace, ancient aliens named after Renaissance painters, and alternate universes? Probably my first sci fi.
Another unnamed book about a girl who was turned to stone either at the beginning or end. I think she was accepting of it which made it merely melancholy instead of terrible. There may have been a smog monster involved but I suspect I got it confused with another book.
Another unnamed book about some kids who fight aliens who have no creativity. There's a magic remote and Baba Yaga, too! I think the title was an acronym but I'm not sure exactly what it was. Something about geeks or nerds saving earth? The aliens may have been shaped like trash cans but that doesn't seem quite right.
The Falcon and the Serpent, by Cheryl A. Smith. Someone is stealing the souls of a kingdom's children: they go to sleep and never wake up. I particularly remember the trap set for the protagonist: he must choose to die for what he believes or, avoiding death, spurn his beliefs. From what I recall, this book had enough threads in the background that there could easily have been more set in this world, but Google finds nothing.