The Cardinals won't be going anywhere for a long while, which is actually a good thing.
I could see the NFL moving teams such as the Saints but I can't see them adding anymore NFL teams.
The NFL is large enough as it is, and adding more teams would change the playoff format a great deal. That could cause some massive headaches.
Places I could see taking on football teams though could be: Mexico (I could actually see a team in Mexico. With the turnout for the Cards/49ers game it's worth considering) and Los Angeles.