I'd really like a plugin that would run every X minutes and log all online player inventories to a MySQL database, assuming that inv has changed since the last snapshot. It would have a field setup like: playername world whensnapped invslot0 invslot1 invslot2... etc Inv slots could be like item ID:qty:metadata. The config file would have parameters to set the interval for snapshots and a max age in minutes to retain. Every time the interval strikes, it would do a delete of records older than the threshold to keep the table size reasonable. I've had some issues with MultiInv wiping out player inventories (then I have to respawn items based on what they tell me) or people claiming someone stole something, etc etc. Something like this would be handy to be able to see what ppl had when.
If you know java basics you could try doing it yourself with CommandHelper, a plugin for programming your own commands and other stuff. The inventory of specific players can be checked and written to a MySQL database or a textdocument, but you would have to figure yourself out how (CommandHelper Wiki).