I've been picking through Highsmith's work here and there, and as many well know, The Talented Mr. Ripley is a classic thriller. Tom Ripley is a model anti-hero, disconcertingly sympathetic even as he's drowning a pal and assuming his identity or thudding the friend of a friend over the head with a heavy ashtray to kill him. Highsmith may have been one of the first to evoke a psychopath so clearly and dispassionately; I saw a bit of her influence in Alissa Nutting's Tampa, where the character of Celeste is a well-drawn predator with a lack of remorse similar to Ripley's own.
Highsmith's life was colorful in its own right; in Carmela Ciuraru's Nom De Plume, I seem to remember an anecdote about Highsmith (who used the pseudonym Claire Morgan to write The Price of Salt) smuggling snails into a country by nesting them in her bosom. Joan Schenkar's The Talented Miss Highsmith is calling to me from the shelf, but it might have to wait until I read the rest of the Ripley books.
