www.decisive.is is a rather good one, but there are tons of them.
Otherwise, the obvious suggestion outside of the search arena is Facebook. Advertising on FB does work, and it's insanely targetable.
Note: none of these options are exactly fire-and-forget - you'll need to put time into learning how they work and optimising your campaigns in order to reap rewards.
I've always been curious about advertising on Facebook, and wanted to give it a try, but my team didn't welcome it. How does it perform against Adwords with product ads?
That being said, you can check out these ad networks. I get the sense that they're somewhat stilted in their demographics, but whatever:
- StumbleUpon
- Digg
- I think Demand offers display advertising?
- Project Wonderful
1. Has to be a cost per click ad model. It can not be impression based. 2. Two goals: Cost per visit under $5. Cost per engagement $10. 3. We need the ability to add several layers of demographic targeting. 4. The idea behind exploring new channels is to engage users with great content. Google Search does a good job, but the content may be to to niche.