It's a really interesting field. Not many get rich from it though. It really is a form of architecture. One learns site planning, really. Olmsted who did Central Park may have been the guy to formulate the title landscape architect. Campus site plans are often done by landarchs. Parks, such as Lawrence Halprin's very strong urban water parks done, I think, in the seventies - parks are not always green. Several of my friends in city planning were trained as landarchs. At a closer to home level, we, that is myself and business partner, like to help the owner site the buildings on a property and work out the grading (land contours) if there needs to be any change, site retaining walls if needed, figure out the pathway circulation and what we call hardscape - parking courts, paved terraces, site fountains, design ponds, pools, site and design decks and overhead structures, design pavilions, oh yes, and then screen negative views and enhance lovely views by choice of planting, often developing complex planting plans - all this with attention to the local surroundings, trying to do no harm - we have been known to take a property back to natural grade after developers filled natural water courses with tons of imported soil.
People tend to think of us as the ones who pick which plant to make the hedge out of, schniff.
You can work for a city or practice as one person, or work in one of the big firms that do range of things. I have to go to work now, but I'll come back later and name some big firms with some job examples.
Some beautiful work has been done recently in Napa Valley..
I am thinking first of Peter Walker's handling of the property that COPIA is on (Robert Mondavi's cornocopia of wine and food knowledge in Napa).
Here's a link to this year's American Society of Landscape Architects design awards... it'll give you an overview, with photos of various kinds of projects.
http://www.asla.org/nonmembers/publicrelations/pressreleases/press04/pressrelease071304.htm