Simply put, a buyers list is a list of real estate investors who are regularly looking to buy real estate. They usually are looking for pre-listings and houses that are just coming on the market.
You can use this list of buyers for leads on not only your flips, but houses you wish to wholesale or sell on assignment!
One of the best ways to create your buyers list is to attend foreclosure and real estate auctions in your area. While you are there, you can network and find buyers. It's important to get not only their contact info, but also what type of houses and price ranges they are looking for, and in what geographic areas.
Another way to create your buyers list is through FaceBook. You can find real estate investor groups. Post to them saying you are looking for buyers. It's great if you have a specific property you can mention with this post. Ask them to private-message (PM)...