Grants NM is a great stop. There is a museum downtown which has a 'uranium mine' exhibit below the building - definitely worth a stop.
The El Malpias National Monument is worth a stop - and you pass between part of the lava flow in I-40. The loop down to El Morro NM is also interesting. Makes a nice day off the road.
Of course you have to stop at/ drive through Painted Desert / Petrified Forest National Park in eastern Arizona.