Write From Home has a list of trade magazines for which you can receive a free subscription.
Many writers are experts in certain areas and write for such trade magazines. They could also be used to expand these areas of knowledge.
For instance, I write about agriculture, housing, and similar topics for nonprofit organizations. I plan to subscribe to several of these magazines that appear to carry information that could benefit me in my newsletter work. I'll report back on the usefulness of the magazines later.