My wife, who runs a book review blog[1] in her spare time, has a popular feature called "First Line Friday" where she features the first line of a book from her collection or her co-contributors', as a way to pique interest in the book among her followers. I sent her the link to this service just now and she loved it. She said it will be a great source for first lines for books she doesn't have but wants to feature.

[1] https://jessicasreadingroom.com/