The UN Audiovisual Library of International Law's Criminal Law website (open access) contains the full text of all major ICL treaties, and their Travaux Prèparatoires, together with useful introductory summaries, current status of the conventions, photos, and videos.
The ICC Legal Tools database (open access) includes all International Criminal Court Preparatory Works, including Travaux Prèparatoires for amendments to the Rome Statute to include the crime of Aggression.
Some Travaux are published online and in print form. For example, The Travaux Prèparatoires of the Crime of Aggression is available in the Law Library at KC 218 A4 TRAV, and as an ebook (UniMelb staff & student access), as well as on the ICC Legal Tools database (open access).
The Travaux Préparatoires of the Crime of Aggression by 
The Travaux Prèparatoires of the Crime of Aggression by