a lonely Donjon bookshelf: what should sit next to it?

Okay, so Clinton extended the offer in the main Donjon book and at least a couple of other places that anyone wanting to write a supplement for Donjon would be welcome to. He'd even host it on the Forge Bookshelf for selling, and you'd get alla that profit.

..now I've been mulling over this since I found the game and started mucking about the Forge back in April or something, and I've yet to come up with anything someone could publish that would be really, truly useful.

A lot of the fun in Donjon comes from simply making shit up as you go along. This makes published adventures nigh-impossible for a group past their first session, and most will "get it" before that's even halfway through. The best you can hope for is a bunch of set pieces for the Donjon Mastah to try and work in, but he'll probably get some better, more appropriate ideas on his own. So basically anything with maps is right out.

Monster books? Not really. Clinton's already put one of those out, which you can use to fake a monster (I need a Bleebloo.. this Berserker's pretty close, I guess..); or you can just roll the Donjon Level plus how hard you want it to be for abilities, the old Shadowrun method. Someone might want to work up something akin to 3E's Challenge Rating - except with proper math, not just out-of-buttocks guessing - but you hardly need a whole book for that.

Settings? Enh. Maybe. Maybe maybe maybe. But probably not. I've had the most fun in my games when the players dictate the geography and political boundries. I could see this working if you decided to limit players to a bunch of pre-defined classes and races, and just use the Donjon system after that, but again, losing some of that magic. . .

Soo.. anyone have any ideas? What might be really useful? Is there any kind of "killer supplement" that could be written for Donjon to really get it up there to the public's notice?