AnswerThePublic
Free keyword tool that visualizes search questions and autocomplete suggestions using Google data.
Ubersuggest by Neil Patel
https://neilpatel.com/ubersuggest/
A user-friendly keyword research tool offering volume, competition, and content ideas (with some free daily searches).
KeywordTool.io
Generates hundreds of long-tail keyword suggestions from Google, YouTube, Bing, Amazon, etc. (limited free version).
WordStream Free Keyword Tool
https://www.wordstream.com/keywords
Enter a keyword or website URL to get keyword ideas along with volume and competition estimates.
Screpy Keyword Research Tool
https://app.screpy.com/tools/keyword-research
SEO toolkit that includes a free keyword research tool offering competition level, CPC, and intent data.
Keywords Everywhere (Chrome Extension)
https://keywordseverywhere.com/
Free browser extension that shows search volume, CPC & competition data inside Google Search, YouTube, and more.
Soovle
Aggregates autocomplete keyword suggestions from Google, Bing, Yahoo, Amazon, YouTube, Wikipedia and more.