Business schools in the US are different from law or medical schools (or other graduate programs) in that you are basically "required" to have real world work experience. There are always a few exceptions made for exceptional candidates, but, in general, professional experience (3-4 years) is expected.

I know this is frustrating to some candidates, but I'd urge you to keep in mind the reasons for this. Business schools, especially top schools, want students to be able to learn from their classmates. If all of the students were fresh out of undergrad, they wouldn't have very much wisdom to impart. Also, students are much more marketable upon graduation if they have worked previously (most companies who recruit at business schools expect that the students have a few years of solid experience under their belts). And, lastly, you will be much more focused and know what type of career you want if you have already had exposure to different disciplines.

You can take your GMATs and get a job which will put you on the right track for an MBA in a few years, but, if a top school is your goal, you should focus on getting a good pre-MBA job first!