As far as planes go, an intriguing option is liquid hydrogen. Hydrogen has a large energy density by mass, which is why we use it in rockets. There have been proposals on how current airliners might be converted to run off of hydrogen in the near term[0] for short and medium distance travel. If we can get fuel cell electric propulsion to work at jetliner speeds there is even more potential, as fuel cells can be made more efficient than heat engines.
I think it would be much easier to use methane. Just as carbon neutral if you make it yourself, and doesn't have as many exotic engineering requirements.
I didn't know that about fuel cells though, interesting.
[0]http://www.fzt.haw-hamburg.de/pers/Scholz/dglr/hh/text_2004_...