Internet advertisers are willing to pay for retweets, registered users, if it is a startup - for debugging, for users purchasing their product or service; what else?
(Background: I founded the largest marketplace for direct ad sales. Powers sites like Microsoft, Aol, Gawker, etc)
If you want to sell ads directly to advertisers... that's awesome, but recognize it takes more work than just dropping AdSense on your site. I'm glad you're thinking of it like "how can I attract advertisers (customers) to do business with me?"
I personally don't think gimmicks work well in the long run. It's all about the fundamentals. You are essentially a business (the website) that sells a product (the ad space / ability to reach your audience) to customers (the advertisers).
All the normal fundamentals apply - you have to attract potential customers, sell them on your product, close the business, get repeat business, etc.
So while a gimmick may work to get someones attention, if their experience of doing business with you is terrible they won't buy or won't come back.
We believe the best way to attract, close and keep advertisers is to make your "products" as easy to find and purchase as possible. In the direct ad space, it is way too complicated - often requiring lots of emails and manual effort. Plus they have to find you to begin with.
Some actionable stuff for you to do:
* Do some customer validation. If you want to sell a product (the ad space), how do you know there is a market? Have you talked to potential advertisers about this? Do you have any pre-committed deals? Do your similar competitors do direct sales successfully?
* Have a .com/advertise page and promote it well. You have to let people know you're open for business. Make it easy for people to find it.
* Have a system that makes it easy to place/execute/manage actual ad orders. This is what we do at www.isocket.com. There are other tools for various needs, website sizes, costs, etc.