I. General References

AHEARN Allen and Patricia. Collected Books: The Guide to Values. NY: Putnam, 2002 (the latest edition).
The standard reference to collectible book values; particularly strong for modern authors but surprisingly inclusive and wide-ranging. A must-have reference.

AHEARN Allen and Patricia. Book Collecting 2000: A Comprehensive Guide. NY: Putnam, 2000 (the latest edition).
Gives value for (mostly modern) authors' first books. With useful appendices of author pseudonyms, individual author bibliographies, and First Edition identification. Already slightly dated, but still a quite useful reference.

MOEBS, Thomas Truxtun. U.S. Reference-iana (1481-1899). A Concise Guide to Over 4000 Books and Articles for Researching Art, Books, Broadsides, Ephemera [Etc..].... Williamsburg, VA: Moebs Publishing Co., 1989.
Hard-to-find but extremely useful bibliography of Americana references, very wide-ranging and including many little-known titles. Compiled from the contents of the author's own formidable reference library.