Pride and Prejudice. This has been my absolute favorite movie since I first saw it...about eleven or twelve years ago now? It's just perfect. (Review here.)
You've Got Mail. Such a cozy and charming movie! It's bookish too, which always helps.
While You Were Sleeping. I might even love this one more than You've Got Mail, though I don't watch it quite as often. Some scenes definitely have a classic movie feel, and I love that Lucy is much more of a normal girl than chick flick female characters tend to be. (Review here.)
The Princess Diaries. This is the oldest favorite on my list. It came out when I was ten, and I got it on VHS for Christmas that year, and I've loved it ever since. It's so hilarious and sweet and cheesy and it makes me feel all nostalgic. And Mia is probably the most relatable character I've ever come across...I'm basically Mia (minus the whole princess thing). (Post here.)
Austenland. This is the newest one on the list, but it was an instant favorite and I think I watched it three or four times the first week I bought it. It's so over the top, but this movie probably makes me laugh more than any other movie. (Review here.)
What are the movies you never get sick of watching?