Animated gifs are nice too, they go up easier on image viewers anyways and may not have the graphical degredation associated with flash and vid. Though I'd like to have the bulk video too, and not recompressed from nico-nico/Youtube either.
Danbooru (the software, like "Mediawiki") is actually a file archival system that can be used to organize business documents and such, so I think any filetype is possible. The practicality is debatable in various cases, though.
