Either fuel cells or batteries will start being used once oil supplies start to dwindle. The energy to take the hydrogen out of water or some sort of fossil fuel still requires energy from power plants. This reduces pollution in cities and along roads. In the US natural gas will probably be done as a fuel for power plants around the same time as gas stops being used in cars, coal will likely stick around, also nuclear, hydro, solar, other.
A big ion engine or nuclear engines would only be used to carry people if there was a big space infrastructure like bases on the moon/mars or for probes going to the outer planets. Chemical rockets aren't that bad for the first manned missions to Mars.
Escape pods would only work in earth orbit. THey wouldn't be bad though.
Nanotechnology is more of a field. There are still some more foundational advancements before we reap the true benefits of nanotechnology.
If there was some new invention that allowed us to cheaply manufacture stuff on the molecular scale that would blow the other 3 out of the water. That would lead to carbon nano-tubes and other carbon structures, these could superconduct and remove heat extremely well this would be a boon for electronics. If molecular machines could be developed that would be a ground breaking advancement too. The aplications and benefits of mature nano-tech would take us very far.