Oh, Children on the Oregon Trail ... the ending is just so emotional. A complete hankie-fest.
I had so many on here - Mary Plain, The Changeover, Sam Pig, Five Dolls in a Dolls House, the Gemma books, all the Melendy books (still love those), all the Lorna Hill ballet books.
A few that haven't yet come up -
Miss Happiness and Miss Flower by Rumer Godden - about a girl who makes a Japanese doll's house
The Case of the Silver Egg by Desmond Skirrow - this one is really obscure, no one I know has heard of it - a detective adventure caper
Trillions by Nicholas Fisk - aliens in the shape of multiplying gems
Re the blind boy trapped in the mine who makes contact with a spirit, I think that might be Annerton Pit by Peter Dickinson, one of my all time favourite authors
Finally, The Guardians by John Christopher, dystopian future in which Britain is divided into cities and countryside with Berlin-wall like fences in between.