What are the other sources to do keywords research other that Google adwords keyword planner?

Below are the best keywords tool that are available

FreshKey

Soovle

Ubersuggest

GA Search Term/Query Reports 

WordStream’s Keyword Tool

Competitor Source Code

YouTube Keyword Tool

Wordtracker

SEO Book Keyword Tool

Keyword Eye

MOZ

KeywordSpy

SEMrush

Keyword Discovery

Advanced Web Ranking

We can do keyword research by checking with competitor domain name also in the Google Keyword Planner.