The Party Storage Chest is the only container that can be used to store party items. In Dragon Age: Origins it requires the Warden's Keep DLC and can be found at Soldier's Peak after completing the DLC's main quest.
The chest does not appear until you leave the area. When you return, it can be found next to Levi Dryden's new shop.
In Dragon Age: Origins - Awakening a storage chest will be located in Vigil's Keep - Throne Room.
Bugs/Inconsistencies
Some weapons and armor that are left in the chest will be re-scaled (see Materials) to the Warden's current level. This can be used to "upgrade" a favored weapon or armor that was picked up early in the game. This will only occur with items that have multi-tier versions; unique items such as the Juggernaut Armor only have one version. Low-level Wardens should be cautious when placing items in the chest, as it can also downgrade them.- For more accurate information on this bug, please see the Exploit listed here.