Private Label Rights (PLR) are the best type of rights you can obtain as far as freedom with what you can do the the products.
Make sure you read the licence conditions thoroughly as there are a myriad of different types of PLR ranging from the unlimited to quite a limited licence.
If you are at all unsure then contact the author or licensee to make sure you can do with the product what you intend to do.
There is a short list of the latest PLR products on this page and a more intensive list on the product pages.