OpenX Ad Server is a powerful open source platform that manages advertising for more than 150,000 websites in over 100 countries. More than 300 billion ads run through OpenX Ad Servers each month. And since it's available as a software download or as a hosted service, you can decide to run it yourself or let us take care of managing the infrastructure for you.
We'll about a month ago, my friend sent me a link to OpenX and when i looked at it i couldn't believe it. Your own free adserver and i've given it a test and its pretty amazing for free as well!

You can have prehosted server or host it on your own server and all for free!

OpenX. Build your business here. | OpenX