August Cover Wars is already closed for new sign ups, but you can get a last minute entry. All you have to do is buy the following Thriller. It's only 99¢, but the price goes up to $2.99 in just two days (Kindle Countdown).
Once you have bought a copy, Amazon will send you an invoice email. Forward that email to me, and I'll put your book into August's Cover Wars (just Cover Wars, not the Scavenger Hunt). If you are already in August Cover Wars, I'll put you into September. I probably won't notice that unless you tell me.
Also, let me know which book you would like to be in Cover Wars.