Since this thread is getting pretty heavily devoured by the "Movie Quotes" thread, I think it'd be better to focus on voices/personalities that get imitated rather than just lines.
Yes. This thread's more about the voice. But of course the quotes often go with the voice. Here it can be about the voice doing the quotes or the voice saying other things as long as it's the voice.
This is really stupid, but many many years ago I put a Darth Vader message on my answering machine (using a glass aside my mouth to enhance the simulation). And last year, when dealing with one of those IRS phone scammers, I did the whole call with Heath Ledger's Joker voice - I didn't start resorting to lines until the end... "
You know, you remind me of my father..."