I'd like to see a really strong general book about bronze age Europe with material useful for other bronze age fantasy stuff like Conan and Glorantha.
I'd also like to see a really solid, powerful piece of NPC/monster generation software to help DMs stat out NPC and creatures in encounters. I'd ideally like to see software flexible enough both to allow maximum detail and customization while at the same time having the capacity to spontaneously generate creatures with very little data for unexpected encounters. I don't see this as being especially hard to program gut I would imagine the task would be quite laborious; still, I can't think of a D&D thing I wish for more frequently.
Finally, a new Deities and Demigods properly re-done to read more like Greg Stafford's Cults of Prax and Cults of Terror -- focused on how the church works, what special powers are associated with clerics, how the temple hierarchy is likely to progress, how the church fits into society, etc. Such a book could take the domain powers down to a greater level of detail, with each god granting class proficiencies in certain skills, possibly custom domains to fit specially with the god's nature, etc. It could also include background about how different gods are in conflict with eachother and how this shakes down at the temple to temple level.
Finally, I'll agree with Phaedrus; I'm tired of making my own maps; besides, with places other than dungeons (town squares, alleys, mountain passes), one often needs a detailed map and has no experience with trying to map such a thing.