What field of Engineering should I go into?

it depends on what you want to do and how you want to get there.
in general, most engineering can be broken down into a combination of mechanical, electrical, and chemical engineering. Mechanical deals with mechanical factors such as stress and friction. Electrical deals with electronic things like circuits, chemical deals with various chemical reactions.
Other forms of engineering build on these. Civil engineering deals with buildings and infrastructure and uses a lot of the same skills as MEs. Computer engineers are basically specialized EEs. Materials science, while very different in practice from ChemE still uses a lot of chemistry. Aerospace (which is what I do) is just ME with more thermo. Petroleum engineers are usually just aerospace engineers who decided to make more money.
There are also more specialized/exotic forms of engineering, like nuclear engineering, that really go above and beyond what your average engineer learns. It is rare that an undergrad college will have a program in these, usually you would do something similar and then go to grad school for it.
Finally, there is the odd ball which is biomedical engineering. This is really just the art of applying engineering to the human body. The vast majority of people who major in BME are pre-meds who think it will help them get into medical school. It won't. There are lots of interesting things that BMEs do, however it is my understanding that most undergrad BME courses don't teach much engineering because they tailor their programs to the premeds. Thus if BME interests you, study something else and then go to grad school for it.
Additionally, there are "soft" forms of engineering like systems and industrial engineering, which deal heavily with things like aesthetics or management. Don't get me wrong, they are difficult and require lots of technical prowess, but unlike other forms of engineering, you don't necessarily have something you can hold at the end of the day and say "I built that", so most people don't naturally lump them in with other forms of engineering.
Most colleges have an undecided engineering program that will show you the basics of engineering. Every engineer on earth has to learn the basic physics, chemistry, thermodynamics, circuits, computer programming, etc and this fills up the first year or two of most undergrad programs.
If you still can't think of a specialty, I would go with mechanical engineering. It is the most general form, and you can go from it to pretty much any engineering grad school program, assuming your other credentials are sufficient. It is also the most widely hire-able, as anyone who is looking for general engineering will take MechEs. That said, MechEs have the one of the lowest starting salaries of any of the major forms of engineering, but it's not much lower (as of 2007: 54k for ME, 55k for EE, and 59k for chemE) and things like internship experience will play a much larger role in determining what you make.
Just remember that there are no wrong choices. So long as what you do, you find interesting and rewarding, you'll be fine.