Atar has a few markets which may be of interest to the souvenir hunter and prices tend to be lower than [Chinguetti] although bargaining is of course expected.
Many of the oases and other natural sites in the region can be seen in day trips leaving from Atar. Ask around at your hotel/auberge to arrange bush taxis, 4x4's, or rent bikes. If your feeling adventurous wander into the market and you will doubtless get offers of obliging drivers ready to show yoy what they consider to be the most interesting sites.
