I actually am
against more adventures/monster books, etc. I think we need more of the
little stuff, and the things that are
missing in terms of "What can you find out there?"
1) Book of Terrain Features. Just open up the
DMG to the terrain features section, and come up with mundane and fantastic terrain. Anything you can drop into an encounter to just make the encounter more intriguing.
2) Book of Locations I: Encounter Locations. This is an elaborate room or area with lots of mechanics to it. Like a clockwork room with rules governing how it works that can be exploited, or used, that effect the place every round. Being swallowed by a great beast, and fighting the contents of its (still moving) last meal. Designs of cool
areas that DMs can put their monsters in and send their PCs to. We have buckets of monsters, but not enough cool places to put them.
Book of Locations II: Fantasy Locales. This is different from the above in that it's not limited to just a place for fighting. These are sites where you might meet a friendly NPC, or explore. Places that evoke a sense of wonder, or get your juices flowing. A magical grotto with crystaline flowers. A river that flows straight up. Each one gets a trio of adventure seeds "Here's why your PCs could come here".
3) Book of Fluff. That's right. Pick a monster and fluff it up. Provide the stuff that many is missing from the
MM. Either with a "Classic X Revisited" ten page spread, or just 2-3 pages per monster. Considering the amount of people that complain about this, it should sell like hot cakes.
4) PDF How-to guide to My Prefered Gaming Style in
4e. You want Simulationism? What about an economy? You want the martial power source to make sense? You want magical items that aren't too watered down? Many out there like X of
4e, but hate Y. A game company can easily pick something that
4e doesn't deliver on, and run the system through the screws mechanically to balance out the material for those DMs who want to do X in
4e.
Once some of those hit the market,
then I'd like to see:
5) Adventure Paths. Preferably one path per tier.