Hall, James. Dictionary of Subjects and Symbols in Art. (2008)
Best small handbook for western art.
Avery Reference N7645 H1411

Iconclass. (Online) (URL: www.iconclass.nl)
An iconographic classification system devised by Henri van de Vaal and used in several photographic archives, e.g. the Decimal Index of the Art of the Low Countries, the Marburger Index, the Witt Library, the Getty Photo Archives, etc. The Iconclass system has been published in paper along with a systematic bibliography arranged by iconography, 14 vols. + 3 vol. index (1981-85).
Avery Reference N7640 Aw11 (Paper)

Lurker, M. Bibliographie zur Symbolkunde. 3 vols. (1964-68)
Interdisciplinary. Continued by title below.
Avery Reference N7640 AL97

Bibliographie zur Symbolik, Ikonographie und Mythologie. (1968- )
Continues the preceding.
Avery N3 B47

Bober, P. and R. Rubinstein. Renaissance Artists and Antique Sculpture. (1986)
Based on the Census of Antique Works of Art and Architecture known in the Renaissance. {In section 12}
Avery NB85 B634

Lexicon Iconographicum Mythologiae Classicae. (LIMC) 8 in 16 vols. text and plate vols. (1981-1997)
Covers Mycenaean to Early Christian. Entries in language of author (Eng., French, German, Italian). Updated bibliography can be found online on a German website at http://www.rzuser.uni-heidelberg.de/~m99/.
Avery Reference N7760 L59 (copies available in multiple locations)

Lexikon der Christlichen Ikonographie. Ed. by E. Kirschbaum. 8 vols. (1968-76)
Standard dictionary of Christian iconography and the saints.
Avery Reference N7645 L59

Index of Christian Art Database. (Online 1991 to date)
A huge photographic archive with a thematic index in card catalog form. Reproduces and indexes all Christian art up to 1400. Online version rarely includes illustrations.
At Princeton University (Paper, 1917 to date )

Réau, Louis. Iconographie de l'Art Chrétien. 6 vols. (1955)
Avery Reference N7640 R23

Schiller, Gertrud. Ikonographie der Christlichen Kunst. 5 vols., index vol. (1966-91)
Avery Reference N7648 Sch33

Schiller, Gertrud. Iconography of Christian Art. 2 vols. (1971-72)
English transl. of vols. 1-2 only of above.
Avery Reference N7648 Sch332 (copies available in multiple locations)

Kaftal, G. Saints in Italian Art. 4 vols. (1952-1985)
By region. Each vol. has separate title.
Avery Reference N8080 K115-118

Rubinstein, R. and P. Bober, eds. Renaissance Artists and Antique Sculpture: a Handbook of Sources. (1986)
Avery NB85 B634

Tervarent, A. Attributs et Symboles dans l'Art Profane, 1450-1600. 3 vols. (1958-59)
Based on The Census of Antique Works of Art and Architecture Known in the Renaisssance {in section 12}
Avery Reference N7645 T67

Van Marle, Raimond. Iconographie de l'Art Profane au Moyen-Age et à la Renaissance. 2 vols. (1931)
Avery Reference N7640 M34

Zappella, Giuseppina. IRIDE: Iconografia Rinascimentale Italiana: Dizionario Enciclopedico: Figure, Personnagi, Simboli e Allegorie ne Libro Italiano del Quattrocento e del Cinquecento. (1992-)
Avery Reference N6915 Z17

Pigler, A. Barockthemen. 3 vols. (1974)
Classical and Biblical iconography only. Illustrated. References to further illustrations.
Avery Reference N7640 P621

(Here are samples of books on non-western iconography.)

Eberhard, Wolfram. A Dictionary of Chinese Symbols: Hidden Symbols in Chinese Life and Thought. (1986)
Starr East Asian DS 721 .E32613 1986

Stutley, Margaret. Illustrated Dictionary of Hindu Iconography. (1985)
Avery Reference N8190 St98