Literary quotes that can be used as e-mail sign-offs?

I work in book dealing and publishing, and am gradually building more frequent correspondences with clients and customers. Recently realized I consistently end my emails with the typical "warm regards," "best," etc, to the point where it's sounding insincere and pretty much just parroting emails that clients are sending me. I know, I know, I'm probably overthinking this, BUT every now and then I'll come up with something from a book or author that I know a client is into and almost always get some kind of enthusiastic acknowledgement on it when they write back. So I thought, why not have some fun and just do this with all my emails? I started collecting quotes while I'm casually reading and want to build an extensive list so I can randomize it with each email.

• "I can no other answer make but thanks, and thanks." – Shakespeare, The Twelfth Night
• “Mind the gap.” – Douglas Adams, The Hitchhiker’s Guide to the Galaxy
• “With all due respect and proper punctuation.” – Lemony Snicket, The Beatrice Letters

You get the idea. Anywat, it's a fun job, and I have the flexibility to be somewhat informal with clients, but I'm starting to feel like a bit of a drab robot and Google is offering little inspiration outside of sentimental and inspirational quotes one might expect to find in a get well soon Hallmark card. So here I am, consulting the human database. Hit me with some media quotes (books, movies, tv, writers, etc…) that can jazz up "Dear Client, Here's a summary of what I did for you today, followed by what I plan to do for you tomorrow. Don't forget to pay me. Warm Regards, Frankie."