On my site I have one banner at the top of each page all hosted from a third party advertising company. The reason I choose to go down this road was simply to make it simple and know that i always have advertisers. Now my page impressions are pretty reasonable and i am concidering selling the ad space myself. My site is a small scale family friendly web directory and search engine so i am able to offer pretty targeted advertising as well as general advertising on my main site pages. What you need to remember is that my site is more of a hobby than a business and should I go down this road. To be honest i am still toying with the idea any info or advice would be gratefully received.