I had this addon at one time which told me how many of the items I had in my vault, alt, bag etc. All I had to do was mouseover an item at vendor and it would display it in the tooltip. (5 in bag) (5 in bank) (5 in guild vault) So for example if was to mouseover a crystal vial it would tell me I already had 5 in my bag (or bank,alt,vault) Does anyone have any idea which addon this is?

armory

http://www.curse.com/downloads/details/10061/

O does that works?

Doh, what he asked for is the only thing Armory doesn't do :(

I know Bagnon Forever has this function, minus the guild vault. Keeps track of inventory across toons, and bags are remotely viewable. Also looks tight, and has fancy uni-bag functionality.

Try Bankitems, its what i use to do that very thing.

http://www.curse.com/downloads/details/11882/

arkinventory