IMHO every good witchy household needs a stock of herbs!!!
But in this day and age with herb shops popping up everywhere what to get can be really quite overwhelming!!! So here is my list of the basics, most of which can be easily grown or readily found at a local supermarket.

Bay Leaves - prosperity
Cammomile - for happiness and feminine complaints
Cinnamon - comfort
Comfrey - healing
Heather - good luck
*Henbane - banishings
Lavendar - for relaxation, dreams etc...great in dream pillows and baths
*Mandrake Root - banishing of a personal kind
Mugwort - for metapyshical cleansing and protection, use with water on scrying mirrors and crystal balls
Red Peppers - to speed up a spell
Rosemary - the "in a pinch" substitute for everything!
Rose Petals - love
Sage - for smuding, cleansings and clarity
Vervain - another protective herb, great in a pot outside your front door

*With these two herbs in particular please use extrodinary caution! Mis-use can easily cause comas and even death.
Be sure to keep both of these well out of reach of children and pets!!!