There are a variety of third party sites that offer Drupal-related information and functionality. For more general reading, you may also want to read the aggregated postings from hundreds of Drupal-related sites via Drupal Planet.

General
Drupal Sites: a directory listing of Drupal-powered sites with tags and ratings

Themes
The Theme Garden: a site allowing you to demo many of the themes listed for download in the contributed themes section.

Podcasts and video
Lullabot Podcast: a weekly audio podcast, 30 to 90 minutes long, about a variety of different Drupal topics, from geeky to super geeky

Drupal community
Groups.Drupal.org: home to user groups, module- and topic- specific working groups, as well as Drupal job postings

API documentation
Drupal Contrib includes a lot of API documentation for the hooks provided by contrib modules

Note: these are a few selected resources that are maintained by the community. This is not meant to be a link farm or other resource to raise the page rank of the linked to sites, but rather a pointer to a handful of sites that have already proven themselves generally useful. Typically, personal or company blogs / sites are not included unless they have extensive "how to" or supplementary information. If you believe your site fits this criteria, feel free to submit an issue to the https://www.drupal.org/project/site_moderators queue requesting you be added with details about your site. A site maintainer will review it and approve it if appropriate.