Professional Photographer magazine has published a review of the X-Keys Professional customizable keyboard. Designed to be used along with your regular keyboard, the X-Keys Professional is roughly the size of an iPad (although thicker). It provides 58 additional keys that can be programmed with customized keyboard shortcuts to perform various actions within Photoshop, other applications, or your computer operating system. 

The X-Keys Professional is available in versions for Windows or Mac and carries a suggested list price of US$189.95 in the U.S.