Classics

• DGE (Diccionario griego-español) abbreviations
  Extensive list of  abbreviations for authors, papyri, collections.  Issued in parts and supplements.  Not searchable. 

• L'Annee Journal or Series Browse

• Liddell & Scott's Greek English Lexicon, 1940 edition
  From Perseus Project.  Abbreviations of ancient works.

• Papyrological abbreviations 
  Extensive list from Papyri.info.

• TOCS-IN (Table of Contents of Journals of Interest to Classicists)
  Journal abbreviations.

PRINT ONLY:

• Dictionary of bibliographic abbreviations found in the scholarship of classical studies and related disciplines / Jean Susorney Wellington. 
  Rev & Expanded.  Westport, Conn. : Praeger, 2003.