It's not really a diary, but Peter McConnell, the lead musician for Grim Fandango, officially released three of the songs from the game along with a description about them. These can be found here.
When Tim Schafer was designing Grim Fandango, he wrote some diary entries on the LucasArts website, but seeing as that's gone now, we've reproduced them here:
Well, "a fish rots from the head down," they say, and for some reason, people always say they think of me and Grim Fandango when they hear this expression. Probably because I love fish so much! You probably didn't know that but, boy, do I love fish! And that's just one of the fascinating things about me that you can learn by reading my personal and private diary where I tell the dark secrets of what really goes on in the halls of LucasArts! From the dangerous hazing rituals to the unexplainable paranormal phenomena that we see here every day, the Grim Fandango Designer Diaries TELL IT LIKE IT IS! Read them before the government shuts them down!
Read the rest of the diary »