Subject Headings:

Classical Dictionaries
Civilization, Classical – Dictionaries
Ancient History – Dictionaries
Greek Language - Dictionaries – English
Latin Language – Dictionaries -- English

The Oxford Classical Dictionary, ed. S. Hornblower and A. Spawforth. Oxford ; New York : Oxford University Press, 2003.
Perkins Reference Desk -- DE5 .O9 2003.  Also available online.

A Dictionary of Ancient History, ed. G. Speake.  Oxford, OX, UK ; Cambridge, Mass., USA : Blackwell Reference, 1994.
Perkins Reference -- DE5 .D53 1994
Covering 776 B.C. to 476 A.D., this fairly comprehensive dictionary has a focus on history but does not exclude any topic except mythology.

Greek-English lexicons/dictionaries may be found in Perkins Reference PA445.  In addition to standard editions, we have Smyth's Greek Grammar, a lexicon of Greek in the Roman and Byzantine periods, and modern Greek dictionaries (at P. Ref. PA1135). 

Latin-English lexicons/dictionaries may be found in Perkins Reference PA2365.  In addition to standard editions, we have Wheelock's Latin, medieval Latin dictionaries including Du Cange, etymological dictionaries, and corpora of inscriptions.  We also have the complete Thesaurus Linguae Latinae in Perkins Reference Oversize PA2361 .T4 1900 and online.

Dictionary of bibliographic abbreviations found in the scholarship of classical studies and related disciplines, J. Susorney Wellington.  Rev. ed., Westport, Conn.: Greenwood Press, 2003.
Perkins Reference -- PA99 .W44 2003.
This is an excellent resource for deciphering abbreviations of journals and other publications, especially older and highly specialized publications.