Well, technically, one came with an author promotion membership I signed up for.
I used The Kindle Book Review for Save the Date! and I used Book Tweeter for Marking Territory. Both were scheduled for 3 days, both beginning June 15.
I've always been hesitate to pay for advertising because it's something that isn't guaranteed. But I decided to try it because the prices were reasonable ($15 and $12 respectively). Plus, I want to eventually quit my job so I can write full-time and stay home with the kids. Since it's not something I've tried before, I decided to give it a chance.
Once I get results, I'll update the post so stay tuned...