Well, I'm not a huge fan of popups myself - BUT - being in business you have to try different things to see what works for your business and your target market.

Popups DO work, unfortunately. Data proves it. Yes, they are annoying to some people - note many people who might get annoyed with popups have marketing knowledge to some extent - regular folks don't find it that annoying.

Dan Zarrella tested popups and found that bounce rate remains the same pretty much, but subscription rate goes up a lot. Judge for yourself
http://danzarrella.com/my-data-shows-email-popups-work-and-dont-hurt.html#

Am I advocating for the use of popup? No, I'm advocating for understanding your business objectives and knowing your target market. If popup helps you achieve your business objectives without upsetting your target market, than go install a popup and get subscribers.

Make sure your offer is superb, and don't spam them with sales emails once they sign up. Respect the subscriber and their inbox. Deliver value!

As for services, these are some of the popular ones:
- https://optinmonster.com/
- http://pippity.com/
- http://popupdomination.com/
- http://ninjapopups.net/

Just a few to name and check out. Optinmonster has great, easy on the eye optin popups.

Remember, TEST, TEST, TEST. If it doesn't work, great. You know it doesn't work. Don't just take people's naysaying and roll with it. They mean it well, but testing is key!