Oxford University Press / NetLibrary.
Available online. (W&L subscription)
Subtitled A Guide to Finding, Reading, and Understanding Scholia, Commentaries, Lexica, and Grammatical Treatises, this 2006 volume by Eleanor Dickey contains discussions of individual ancient authors on whose works scholia, commentaries, or single-author lexica exist, together with explanations of the probable sources of that scholarship and the ways it is now used, as well as descriptions of extant grammatical works and general lexica.