I have found that one of the best things to use a little later in the game is aircraft carriers filled with bombers. Especially if they do not have a strong Navy. You can bomb their resources deep in the territory, isolate their capitol and bomb selected units that would be difficult to get to either within your own borders or just inside theirs (artillery). Even trying to pillage resources with fast moving tanks would leave them vulnerable to counterattack since generally it takes more than one turn to reach their resources. Also, if you are being attacked by their Navy, you can bomb them down initially using either artillery or bombers so that they don't attack your weak carriers. Of course I modified the movement of the carriers so that they are more useful, but I have knocked back a couple of civs to ancient times by bombing just about every improvement they have.