It can take weeks or months to see your book on the most popular newsletters, but the publicity is worth the wait. (blog.infinitypublishing.com)
Below is a list of some of the most interesting and popular newsletters on the web today. (policygenius.com)
Though, I couldn't find the numbers on how popular their newsletter is, the Indie Next List section on their website has an Alexa rating of 5,000 globally which isn't bad. (writingbytheseatofmypants.com)