Overdrive has expanded upon a new program called Test Drive that allows libraries to lend out hardware for their customers to borrow. The ever popular iPad 2, the ever-inexpensive Agasio DroPad A8i, and the ever-versatile Toshiba Thrive. Most of these are rather expensive and I would recommend the sole dedicated e-reader the company offers, the Sony PRS-T1.
All of these tablets available to libraries for purchase for their customers give you a big bang for your buck. The Thrive and DroPad have access to the official Android Market to download and install apps. Each model will come bundled with the Overdrive Application on the tablets giving you full access to the ebook and audiobook downloads.
To be clear Overdrive does not sell or lend devices out the libraries must purchase it themselves and the company will provide the software and information on how to customize it for the library environment. Check out some of the partner resources HERE.