Heartwood Ring

Heartwood Ring is an magical ring which can only be worn by druids which adds one level 6 and 7 priest spell slots. This item appears in Baldur's Gate II: Throne of Bhaal and this item will probably appear in Baldur's Gate II: Enhanced Edition. Cespenar can make this ring by combining Nymph's Tear with an Oaken Ring and paying some gold for the service.

In-game description
"Combined with the Nymph's Tear, this simple band of oak allows a druid to draw upon the natural energies of the world around them."