Chaco Canyon and Shiprock in the NW corner of the state.
...and if you are up there, I'd hit Mesa Verde as well, rather than Taos. It is closer (and way more interesting, IMO). If you have some extra time, you might travel U.S. 550 between Farmington and Cuba. It is a beautiful landscape. There is also a dirt road, 126, that goes from Cuba eastward into the mountains west of Los Alamos. I tried to go that way on my recent trip (actually headed into Cuba, not away from it), but it was closed halfway in due to winter weather. I would like to go back to that road some day because it was so beautiful.
As for general suggestions, don't break the speed limit by more than a few miles per hour on native reservations. I saw way more people pulled over on native land in NM and AZ than I did anywhere else on my cross-country trip. Wear a hat and sunscreen (neither of which I had last time, as it was winter and I was not spending a ton of time in any one place), and make sure you have plenty of water. Make sure you don't leave your film in a hot car.
As for film, you might want a color film in addition to Velvia, but that is up to you. If it has to be Velvia, perhaps the think about the 100F, as it more easily captures a high-contrast range.
White Sands is nice, but hardly northern NM!