We have done a number of unusual partnerships at our library. Here are a few:
For our general ongoing sponsors of our community reading program, Amarillo Reads, we got Hastings, a national chain of book and music stores, and our local newspaper. Hastings supplies books for author book signings, provides coffee and staff to run the book signings, and supplies plenty of copies of the books at all their locations in town. They also use their clout with publishers to help us get authors for next to nothing! The newspaper gives us free advertising space, so people will know what programs we're doing and what the book is.
We do Amarillo Reads four times per year, and the Fall one is by partnering with the Amarillo College Common Reader program. They choose the book, pay for the author visit, and ride herd on the author, and we do displays and events at our locations, provide the setting for the open-to-the-public author event, and help host a VIP reception prior to the event, and the booksigning after the event.
Other partnerships we've done: Getting the local opera company to do an opera based on the book we'd selected (Cold Sassy Tree), getting the local herb society to do an Herb Growing and Cooking event in association with a book selection, having a local bakery donate cupcakes and decorations (and instruction) for a cupcake decorating event. We've also used lecturers from local universties, the local chess club, railroad artifact society, storytelling groups, and local theatre groups. We've even used the local Native American Drum Group and tribal elders for events. And then there's the poetry slam groups for our poetry readings...