NatureServe already has a database like that. They'll share it with you if you give them a good reason to, but they won't just give it to the general public. Exactly what you are advocating. A better endeavor might be to offer to contribute to that database.
While I certainly enjoy the Natureserve website, their applications, and work with Natural Heritage programs, I've noticed alot of them either have an extreme backlog of data or very incomplete data. For the general public, yes it is a great way to get data, but you're just as apt to find it via your state's DNR and/or DEP.