These are a couple of books and documentaries recommended over and over again by people I have talked to.
Convert It!: book by Micheal P Brown, also who also runs Electro Automotive. The book is a bit dated being written in 1993, but still very relevant. Electro Automotive also sells various kits for common conversions such as the VW rabbit and Geo Metro, and generic kits.
Build Your Own Electric Vehicle, by Bob Brandt. Also a bit dated (1994). Goes into more technical detail, more history and more theory than the Brown Book, but less of a step-by-step guide. This is my favorite between the two books.
Who Killed the Electric Car?: a documentary on the rise and fall of the EV1, a technically successful electric car produced by GM in the 1990's. Get out your tinfoil hat.
Links
Here is a compendium of links I put together while researching my EV conversion, roughly organized by topic.