1. Google AdWords: Keyword Planner

The most obvious choice for the top spot, this free keyword tool has been a favorite for many years.
Not only is the Google Keyword Planner a good choice when starting a new site, but it can also be your best friend as you grow and produce more content.
The primary benefit of this tool is easy to see: you’re able to pull information directly from Google, which is the search engine you’re most likely to target when optimizing your website.
The first step is as simple as entering your keyword or keywords into the search box.

2. AdWord & SEO Keyword Permutation Generator

Are you struggling to uncover new keywords in your keyword research?
This is a challenge that you may face when launching your new site. While you’re familiar with the top keywords in your niche, you don’t know where to go from there. And, as you know, that can be a problem as you create more content.
Consider this keyword tool a great way to help.
With the AdWord & SEO Keyword Permutation Generator tool, it’s easy to get creative as you search for keywords that align with your site, marketing strategy and goals.
The thing that I like best about this tool is the way that you can get creative. You can enter a keyword in each of three boxes, hit “generate permutations” and watch the magic happen
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3. Google Correlate

As noted above, there’s nothing better than getting advice straight from the source. And, once again, Google is the source I’m talking about.
Google Correlate is an often overlooked tool that can be extremely powerful for generating a large keyword list.
The primary reason to use this tool is the ability to see which keywords get searched together. With this information, you can begin to grow your keyword list (especially longtails).
In the example below, you’ll see that people who search for “diet plan” also search related phrases: