Flippa is a great place to find, buy, and sell your online businesses, established domain names, and websites. Recently, they have also introduced an option to sell your android and iOS applications as well. 

Websites and apps are categorized into several categories like established sites, starter sites, domain only, most active etc. The prices vary from project to project but on both sides, a seller as well as a buyer, you can expect a good profit you are well prepared for your purchase.