I wandered by the UMD library today and picked up The American Presidency: An Analytical Approach, by UMD prof Irwin Morris (who I don't know.)
Writing about the VP, I need a decent foundation on the study of the president and the presidency. There are endless volumes devoted to the topic. But Morris' book, which is designed as a good undergrad textbook, provides a strong overview of theories and the state of the field.
For background reading, an up to date textbook is a good idea - I wish I had thought of it a few years ago - would have saved me a lot of time trolling around in back issues of Presidential Studies Quarterly.