SRD:Druid's Vestment

Vestment, Druid’s: This light garment is worn over normal clothing or armor. Most such vestments are green, embroidered with plant or animal motifs. When this item is worn by a character with the wild shape ability, the character can use that ability one additional time each day.

Moderate transmutation; CL 10th; Craft Wondrous Item, polymorph or wild shape ability; Price 3,750 gp.