Together:
Novels: Streets of Blood, Nosferatu, and Black Madonna.
Sourcebooks: London, Tir na nOg, Prime Runners
Adventures: Celtic Double Cross
Alone:
Sargent: Imago
IIRC, Black Madonna is the first introduction of Leonardo; I may be wrong. I suspect that Sargent is to blame for most of the crap, but that's just me.