Superman Red/Superman Blue #1 (1998). Its the one-shot that introduced Superman Red, so its definitely a needed book in our Superman Blue/Red oeuvre.
Superman Forever #1 (1998). This is the book that concludes the Superman Blue/Red era and restores Superman to his traditional outfit and power set. Also a definite need in our Blue/Red collection.
Superman/Batman: Secret Files and Origins #1 (2003): The only book from Superman/Batman not available in digital. This needs to change, please.