I ran across Project Wonderful lately.
They’re a service that allows you to advertise on websites. Primarily you’re putting graphic banners or buttons on other websites. They use an auction system, so you bid the amount you want to spend for a particular advertising spot on a particular website, and if you’re the high bidder your ad displays.
You bid on a cost-per-day basis. So if you bid $0.10, that’s for all the impressions that site gets that particular day. You have no guarantee how many that will be, but the site does provide traffic graphs so you can see how many impressions/unique visitors that site has been getting.
In a nice touch, if the website owner hasn’t set a minimum bid, you can actually advertise for free. A $0.01 bid will outbid you, and you can only advertise for free for two days before needing to renew your ad, but it’s still a very niche touch. It’s primarily the lower traffic sites that provide free advertising, but get enough of those showing your ad and you’ve still got a lot of impressions for free.
I’ve done some preliminary testing on some moderate and lower traffic sites, and I seem to be averaging about $0.30 cost-per-thousand impressions, and about $0.02 cost-per-click.
The site allows you to search for websites by tags the website owners use to describe their sites, so you can target your ads pretty well. All in all, the site is very well done and provides a nice advertising service.
On the other side of things, you can use this service to provide hands-free advertising space on your site. If advertisers are getting results, you’ll see the CPD bid up over time.