New music to look for
Although my research is limited to 1550-1612, I'm still listing everything that may add to the full development of the spezzati style. So here are some works I found out about today:
Ignazio Donati - Musica Lontana (not exactly a work, but a style)
Claudio Monteverdi - 1610 Vespers
Michael Praetorius - Syntagma Musicum (1619)
Benevoli(?) - Missa Salisburgensis - 53 voices, 8 choirs
Galuppi (from Venice) - Mass for four choirs and orchestras
Handel - Israel in Egypt
Monteverdi's Vespers and Praetorius' Syntagma are not new to me, though. I'm actually pretty sure most of these are non-spezzati polychoral, but they are heavily under the influence of the spezzati technique, so here they are. I'm actually very interested in Musica Lontana since I've never seen ANYTHING about it. 'Lontana' means 'distant' in Italian, so this seems promissing... (and I'm still to find a link to Ligeti techniques...)
These were found on New Oxford Companion to Western Music, which not only is a great dic/pedia of Music but also was edited by Denis Arnold, a specialist on Cori Spezzati, so yay for that!