Keep checking back for lists and posts about donating books! Lists of charities will be listed on this website. Websites that promote book donations and contact information of organizations that take donations will also be listed.
Exhaust all outlets for promoting your book drive. Create an evite or zvite.com. Create an event on Facebook and invite everyone. Tweet your event, write a blog post on it and encourage your blogging community to spread the word too! post flyers around town, at libraries/schools/bookstores/shops/restaurants,government buildings notify your local newspaper/new station/radio station. This part is real important--get PERMISSION first before you post anything at a place of business or private property. Post something about it on Craigslist. Tell local churches and organizations about it and recruit volunteers.
After all that is done, let me know about your event and I'll do my best to promote it too!