Probably not insider info, but I would say Nevada, New Mexico, Arkansas, and Mississippi would be right in the mix if you're looking for a large person to doctor ratio. Also, I'm sure Alaska and Arizona are up there as well.
I would look at the national health service corps job search site. http://nhsc.bhpr.hrsa.gov/jobs/search_form.cfm These are underserved areas. I also know that Georgia is one of the most underserved states and that you could set up practice in the nicest part of Atlanta and do very well.
Minnesota. I guess that's one of the reasons they're beign more flexible with foreign trained dentists.
Arkansas, sort of. On the ADA website, some time ago, I read they're having a growing demand for Spanish speaking dentists, and due to this are thinking of being more flexible with foreing trained Spanish speaking dentists.