I agree with Bruce, Realtor.com is a good resource.

If you are looking for a rental property to rent yourself, then there are other sites in addition to the great ones suggested by Bruce: http://www.apartments.com, http://www.apartmentsource.com, http://www.apartmentguide.com.

If you are looking to buy a rental property then it's just easiest to find a realtor to help you find the right property. But if you want to find the property by yourself, then you can use such sites as: http://www.craigslist.com, http://www.ziprealty.com or any of the big real estate brokerage websites--they usually have MLS search engines available for free as well (e.g. http://www.coldwellbanker.com, http://www.remax.com, http://www.prurealty.com, etc.).

Check out rent.com, realtor.com, and craigslist.com. That’s where you’ll find the most rental listings. You might also check with one of the property managers in your local area to see what they have or will have in the near future.

Rebecca,
you need to be much more specific... Are you from Pikeville or is that where you'd like to find a rental? How many beds/baths do you need? What is your price range? What amenities are important to you? Please re-post your question.