Your Site is like Real Estate
Remember that a website is like Real Estate! Your pages are your lots and the space is valuable. You paid money to have the pages placed on the server and more money to have the pages built. The space has value if the old rule of Location, Location, Location is followed. If you have traffic of 2000 a day or more, advertisers will be easy to find and some will come to you. You can charge for the space like a 125x125 pixel add for $xx.xx number of dollars per month. Location is what type and what niche you fit into. It seems, that sites with a store(ecommerce) is a big draw. It seems like membership type sites are also a big draw. A forum and/or blog helps out as well. Attractiveness also helps as does good content and SEO.