While looking at the articles for herbs here I thought I'd add some more neat uses!
Peppermint/spearmint - Good for keeping bugs at bay in gardens and on animals. Placing the leaves in a chicken coop could deter things like mites and spiders (if your afraid of them or have poisonous ones in your area).
Wormwood - another one good for in coops to deter mites. Satchels placed in nesting areas can deter the little bugs from making it their home.