This might be a nice place to plug Project Wonderful, an innovative bid-based advertising system that's been gaining support in the webcomic world but probably has a future elsewhere, I think. I know I have clicked about ten times as many project wonderful ads since it started about a month or two ago than I had clicked non-project wonderful ads in the ten years I've been on the web prior to that. Since people are buying adspace on YOUR website in particular instead of buying generic adspace that gets rotated with various degrees of targetting, you're more likely to get relevant ads on your website.
Here's a quick rundown on how to sell adspace and how to buy adspace.
I'm not affiliated with Project Wonderful, just a fan of Project Wonderful founder Ryan North