Generally speaking, if a given plugin proves that it's a quality solution and gains some popularity, it will be showcased on the homepage of the official directory in the Featured Plugins section. But if you want to be up to date with things as they happen, you can pay attention to what's going on at https://wordpress.org/plugins/browse/new/.
Additionally, a great way to discover new plugins is to become a regular on one of the popular blogs about WordPress. Although these blogs are not official creations (they are run by independent owners), they do provide an impressive range of tips and advice, not only on plugins but also on other aspects related to WordPress. The list includes the following: