Hello I have a popular site with about 3.5m page hits per month, i have AdSense but would like to start selling ad space on my site, as i believe this would be more profitable than us just selling our products, so the company or person that places an advert would pay us per week, month and so on. I'm not really interested in affiliates and no more PPC, so where would i start, would i have to send a letter to the big companies that are in my niche and ask them if they are interested in placing an ad or do i go to a broker to do this for me? Any advice would be great Thanks
Make some ad zone and create a separate contact page for advertisers. Do provide the rough traffic stats (especially traffic volume and geolocation) on that page. Here is an excellent answer to your post by DoshDosh blog. http://www.doshdosh.com/direct-advertising-sales-beginners-monetization-strategies/
You may want to look at an ads server script or remotely hosted software solution first so that you can easily track the ads per each customer you have.
Why do you not want to do PPC? The big three traffic companies on the 'net sell by the click... interesting isn't it? Put together a sales page and sign people a recurring fee for traffic. If you let your customers know where there ads are actually placed your encouraging click fraud and the quality is going to be bad because they will click on competitors ads.