Recently watched Don't Bother to Knock. It's a 1952 thriller in which a shy and fragile woman is hired to babysit a little girl in her parents' hotel room while the father is getting some kind of newspaper award. Then she turns out to be nuts and dangerous. This is a good one for a few reasons:
1. In what has to be considered a pretty high-quality cast in general (Richard Widmark, Anne Bancroft, Elisha Cook Jr., etc) Marilyn Monroe is a standout as the babysitter. Monroe was a more internalized actress than she was generally given credit for at the time, and I suspect her background in the foster care system helped inform her performance here.
2. There's a pretty bold jazz soundtrack by Lionel Newman, one of Randy's uncles. Bancroft's character sings several songs as well, and either he or whoever she was lipsyncing to had a good set of pipes.
3. Aside from the girls' parents attending the newspaper banquet, the action never leaves the hotel. It uses that setting to the fullest, setting up a varied dynamic between the major and minor characters who work there. Nothing is wasted.
The movie also has a sharp sense of humor about itself. From a certain point of view it's a comedy.