EzekielRaiden
Follower of the Way
This, I think, is the hardest part of the question. It has to be something that essentially anyone with power wants to have. They don't necessarily need it for the same reasons, but everyone has to want it. Some of these beings are already immortal or don't strictly care about death, so that's largely out the window (at least as the main motive.) Several have access to, if not total knowledge, then rather a lot of it, so it probably isn't mere information. It can't be purely magical mojo, since the crime lords wouldn't be able to use it, though I guess they could want it in order to sell it to the highest bidder (but that feels kinda weaksauce.)elder dragons to archmages to crime lords to angelic hosts, that are going to want it.
The biggest problem of all, though, is why the PCs wouldn't just give this thing, whatever it is, to the angelic host, assuming those angels are (non-4e) D&D angels where they're inherently good beings. It needs to be something the PCs can't trust anyone, even angels, to have--and that's a hard bar to clear.