Uttarakhand-Nainital, Ranikhet, Kausani Binsar; Himachal: Dharamshala, Bir-Billing, Kangra Valley; An interesting getaway might be Orchha, Khajuraho, Panna; These places can be built into a 3N-4D trip.
You can cover quite a few places in that period of time. One good trip can be Udaipur and Mount Abu. It depends on what kind of a trip it is, whether you want to go to a place and relax, roam around at leisure, or whether you want to cover maximum places and points.