Choosing the right keywords for SEO is essential, because the keywords associated with your website will determine which and how many Internet searchers will find it. You want to be sure that you’re optimizing for keywords that your target audience is searching on. This is where keyword research comes in. Here’s a quick overview of the best SEO keyword research tools available:

Free Keyword Research Tools

Alexa

Alexa offers a wealth of free search analytics tools that can help you optimize your website. To conduct keyword research with Alexa, you can:

• Type in a search term to find out how popular that query is (“Query Popularity”) and how much competition there is from other websites for that particular query (“Query Competition Index”).
• Type in a competitor’s website to see what keywords they’re using to attract traffic.

Google
Google provides a number of free keyword tools, particularly for those who have created AdWords accounts. An AdWords account is how you buy advertising space on Google, but you can sign up and use the tools even without purchasing advertising space.

• Google Search-based Keyword Tool
  • Google’s Search-based Keyword Tool will suggest keyword ideas based on your website and your Google AdWords language and country settings, so you get suggestions that are particularly relevant to your needs. It provides info on the number of monthly searches and the competition for each suggested keyword, as well as a suggested AdWords bid price. You can also browse keywords by category. (This tool is very similar to the Google AdWords Keyword Tool, but provides a little more data.)
• Google AdWords Traffic Estimator
  • This tool will provide an estimate of how much advertisers are paying to have their ad displayed when certain keywords are searched–keywords with a lot of searches tend to be more expensive. Use the Traffic Estimator for keyword research by looking for keywords that are relevant to your website but are not the highest or lowest priced–the top priced keywords generate a lot of competition, and the lowest priced ones see too little traffic.
• Google Insights For Search
  • Google Insights for Search is how you can find out who is searching for what keywords. Enter your search terms and Google will provide you with an analysis of the keyword’s search trends relative to Google’s total number of searches. You’ll be able to see the change in search volume over time, amount of interest by geographic area, and similar keywords that are highly searched or that have seen an increase in number of searches.

Paid Keyword Research Tools
Wordtracker
Wordtracker is generally considered the gold standard in paid keyword research. There’s a free Wordtrack keyword research tool, but access to the features that make Wordtracker one of the best requires a paid subscription. They do offer a free trial, however, so you can see if you like it before you buy. You might also want to check out the Wordtracker-powered SEO Blogger plugin for Firefox.

Keyword Discovery
Another good keyword research tool which also offers a free trial. According to their website, Keyword Discovery has the largest keyword database, containing nearly 38 billion searches from more than 200 search engines worldwide.