For about 15 years we maintained (on this page you are reading now) a list of the better Business to Business Directories available on the internet. It seems impossible to keep current such a list over any long period, because online directories seem to pop up and disappear with wild abandon.
Only a few years ago, it was important (for good Google rankings) to get one's website listed in as many directories as possible, always in the correct category in a relevant directory. Google no longer seems to care about whether a website is listed in any directories, even though (only a few years ago) it really helped to be listed in the old Yahoo Directory, and DMOZ, and whatever other directories one could find online. The links within those directories to a website used to be "golden." But not now.
Google My Business has supplanted all the old online directories. Register your website there and Google will know your business exists.
The only Business to Business Directory where we still recommend registering your website is Best of the Web. It's been around since 1994, and has a TON of business listed in it. We're in there!
There's a list of the top 100 "directories" maintained by Vendasta. Many of the entities listed there are NOT actually directories (such as Google, Facebook and Twitter!) but if you poke around there you will find some actual business-to-business directories where it might be worthwhile to register your website. Vendasta is making a valiant effort to keep their links list up to date. Consider these directory listings as little advertisements. If you have the advertising budget to get listed in several relevant directories, go for it! That Vendasta page provides a starting point for you to do that.