Okay - two things I can do for you.
For free, I can suggest that you look into advertising providers or start a sponsorship/advertising program of your own.
For a service, I can provide details of several Advertising companies that could supply you with CPM advertising (pays by the thousand for page impressions/hits), which is more reliable than PPC (pay per click).
If you are UK based, I may even beable to recommend up to 3 reliable marketing companies for you.
Ah, sod it - I hate being tight and wanting cash :)
Most advertising companies or online marketing companies havereally shoddy search-engine data, so finding them is a nightmare (go figure).
Look for companies such as Aurora, Doubleclick or Adtech.
I myself would look into my own Sponsorship and Advertising system - as that means you can control what adverts, where they go and how much you get etc.
Depending on what you site is built with/how good you are, you can handle such a thing yourself, (I use Xaraya and use the Articles module ;)).
Alternative, you can use something like adnews or what not to control your own campaigns, and that has instructions on how to include the advert display code.