http://directory.ccnecommunity.org/reports/accprog.asp
http://www.acenursing.us/accreditedprograms/programsearch.asp
The two main accrediting agencies have a searchable list of their approved programs. A program is typically on only one of these two lists.
I read that typically if a program is accredited by one of these two organizations, your state will allow you take the certification exam.
You may find some for profit or online schools claim to be accredited by another organization, that may not be legitimate.