Content Marketing Stack - A curated directory of content marketing resources
KeywordTool.io - KeywordTool.io is the best FREE alternative to Google Keyword Planner and Ubersuggest. It uses Google's autocomplete feature to get over 750+ long-tail keywords for any given query.
Topic Research by SEMrush - Content ideas that resonate with your audience
Google Trends - Explore Google trending search topics with Google Trends.
Content Snare - Content Snare helps businesses collect content and documents from stakeholders - on time, in the right format, without email
Keywords Everywhere - Free browser add-on for keyword volume, CPC & competition