If you have a LibraryThing account, you can easily compare your library with Plath's and see how many books you have in common (I have ten). Also, the good people who added Plath's books to LibraryThing have included notes from the catalogs of the libraries that own the books, some of which are really fascinating -- like the following notes regarding her copy of The Art of Loving by Erich Fromm:
Copy is heavily underlined and marked by Sylvia Plath; bookseller's label: Foyles, London; autograph: Sylvia Plath, Court Green, November 9, 1962.Or this, regarding her copy of The Collected Poetry of W.H. Auden:
p. 19, 30, 37, 97 (Sept. '63)"- note in Assia Wevill's hand below Plath's autograph.
Inscribed on fly-leaf: “I found my god in W.H. Auden”. With bookplate. Underlining and annotation, very heavy in the last sections.I *heart* LibraryThing!