Take initiative to publish your undergraduate research.  Many undergraduate institution have a peer-reviewed journal that publishes the research of undergraduates.  It's not the same as publishing in a science journal peer-reviewed by other scientists, but at least you have shown initiative to the medical school that you did take time to put together the data that you collected over the years into a publishable format.  This is definitely a positive mark on your application and looks better than if you didn't publish in your undergraduate journal.

If you want more visibility, then you may want to consider publishing in Journal of Young Investigators (www.jyi.org).  This is a journal for undergraduates around the world publishing original research in various scientific disciplines in addition to publishing feature articles.  The scientific manuscripts are peer reviewed by undergraduates majoring in that discipline along with a faculty mentor who helps critic the manuscript alongside the undergraduate reviewer.  I highly suggest that you look into this.

Publishing anywhere shows initiative. Especially if you are MD/PhD, try to publish and if not submit your work as a poster at a conference.