20$ in Paypal, where to spend for best results for marketing?

Guys

I am about to receive 20$+ from Domain Parking site where I have parked few domains. I will get payout on Monday-Tuesday. I want to spend this money on marketing my ebooks selling site so I may get some sales.

Please recommend me any thing where to spend this money. I already tried AdWords but that is not much working. Visitors coming but not sales.

Any idea about good Ezine, Safe List, or any other site. Or I can spend 10$ at one campaign and 10$ at other. That marketing should not against AdSense TOS.

I think my ebooks selling site is a good site and I should get some sales. :)

John

Didn't you try some free methods to getting visitors?