During my rest weeks I focussed on stretching and cardio. I did two days of yoga workouts, 1 day of Pilates and 3 days of cardio such as kickboxing and step aerobics. I avoided lifting any moderate to heavy weights to give my forearms a rest.
I agree with Hazlady - yoga and cardio as the go-to workouts. Depending on how I am feeling, I sometimes fit in hiit training in addition to steady state. I usually fit in a metabolic workout using light weights once during the week.
I try to get to some enjoyable outdoor pursuits during my 'fun week' - biking, running, hiking, swimming, tennis, cross-country skiing or just long walks. It is nice to mix it up and have some fun and fresh air!
For my rest week, my main goal is to avoid any kind of strength training so my muscles can rest. I do stretching, yoga, pilates, walking on the treadmill, light elliptical training, or any of my cardio DVDs that are at the beginner or intermediate level.