Work experience is more-or-less critical for the MBA experience and admissions, in particular at the top schools. For example, Harvard recently started a 2+2 program for students applying while still in school. This program basically says, go work for two years, and then come back...
Unless you've done something absolutely amazing while in undergrad, or are the super rockstar of HYPSM, you're likely not getting into a top, top program without experience. You may be able to drift further down the quality totem pole, and target schools in the bottom half of the top 50. The problem, however, is even if you gain admission, recruiting will still be a headache as you'll have no work experience to illustrate your abilities.
In the end, I, and I am sure most, will strongly suggest getting at least 2 to 3 years of work experience prior to entering an MBA program. Good luck.