RENT is definitely a good one. I also love to watch Mean Girls and... my all time favorite that I've purchased on DVD three times because I lost my copy is...
All the Audrey Hepburn movies
Shawshank Redemption (especially when I'm depressed)
Pride and Prejudice with Colin Firth
Forgetting Sarah Marshall
Shakespeare in Love
Pride & Prejudice (Keira Knightly)
The Notebook
CenterStage
Audrey Hepburn movies
An American in Paris
Devil Wears Prada
Something New
Love me if you Dare(French Film)
Love Actually
Notting Hill
Mansfield Park
Don Juan DeMarco (Johnny Depp)
Chocolat
Dirty Dancing
Can't believe I'm admitting this but Harry Potter & The Sorcerer's Stone is my default background movie. I also watch Corrina, Corrina every time it comes on television.