I recently purchased an adbrite clone...well 60% clone. It's not the same but kind of like adbrite. It allows publishers to list their sites and sell ad space. You can sell links per day, per week, month, etc. Advertisers can browse through sites and if they like any they can buy advertising space right on their site. I dont have a domain name yet and it's not set up yet. I am looking for people that would like to help me out and we split the profit. If you're interested in starting a new advertising site please PM me.
In my opinion, it's not worth going into such a crowded market, where almost all of the major players have their own unique system which is doing so well.
The online advertising is the next booming market. What if some big players are already in market. Enter the market, just imagine even if you get .001% of what they get, its quiet enough for us. I'm already having many classified sites, forums i've have a great traffic. Just looking for script similar to google adsense, if anyone knows pm me.