What to read after New Comparative Grammar of Greek and Latin?

Like Carl Darling Buck's Comparative Grammar of Greek and Latin (1933), this book is an explanation of the similarities and differences between Greek and Latin morphology and lexicon through an account of their prehistory. It also aims to discuss the principal features of Indo-European linguistics. Greek and Latin are studied as a pair for cultural reasons only; as languages, they have little in common apart from their Indo-European heritage. Thus the only way to treat the historical bases for their development is to begin with Proto-Indo-European. The only way to make a reconstructed language like Proto-Indo-European intelligible and intellectually defensible is to present at least some of the basis for reconstructing its features and, in the process, to discuss reasoning and methodology of reconstruction (including a weighing of alternative reconstructions). The result is a compendious handbook of Indo-European phonology and morphology, and a vade mecum of Indo-European linguistics--the focus always remaining on Greek and Latin. The non-classical sources for historical discussion are mainly Vedic Sanskrit, Hittite, and Germanic, with occasional but crucial contributions from Old Irish, Avestan, Baltic, and Slavic.