Actually The Talented Mr Ripley was a book a long time befor polanski made his movie.
Nah, “Guise will be Guise” has Wes pretending to be Angel. Nothing can be better than that…
A number of S1 Smallville episodes seemed to be lifting ideas from both BtVS and The X-Files. There was the bug boy, the girl who sucked the youth out of her victims, to name a few. I can’t remember all of them, I just remember thinking after “Nuts to this. I’ve seen all of this done before and better too…”
Not that Joss Whedon didn’t borrow extensively from other sources for BtVS, he just tended to put a different spin on the ideas…