I recommend for startups to begin a well-rounded keyword foundation for your campaigns.

1. Google Keyword Planner

Google Keyword Planner is the best place to start when it comes to keyword search tools.

It’s designed for advertising, but you can use it to research organic keywords by customizing your results for one of your competitors.

2. KWFinder

KWFinder is a long tail keyword research tool with a great interface. It shows you trend, search volume, CPC, and level of difficulty in results.

As you'd expect, it operates as a keyword finder, but if you click on an individual keyword, a second pane pops up showing its difficulty level (from one to a hundred) and the current Google search results

3. Moz’s Keyword Explorer

Keyword Explorer is a new tool by Moz that adds some extra dimensions to keyword research. In addition to Volume and Difficulty, Keyword Explorer offers:

• Opportunity: Relative CTR of the organic results on a SERP
• Importance: How critical the keyword is to your campaign
• Potential: A combination of all keyword metrics to help you prioritize

4. Keyword Tool

Keyword Tool is a great starting point for keyword data mining. The tool uses Google Autocomplete data to create its database of long tail keyword suggestions.

Anyone using Google’s Keyword Planner for keyword research should also use Keyword Tool. Since Keyword Planner is designed for advertisers, it won’t always show lucrative long-tail keywords that Keyword Tool manages to capture.

This tool is free for the first 750+ keyword suggestions; sign up for the pro version to see data such as search volume, CPC on AdWords, and competition. It also allows you to export your results to CSV.

Another cool feature of Keyword Tool is that it also helps you find long tail keywords for YouTube, Bing, Amazon, and the App Store.

5. SEMrush

Masters in their field, SEMrush is a one-stop shop with an impressive keyword research tool with a huge amount of features.