Where to get list of keywords for Google Adwords campaign?

The most important item in internet marketing is to get the right keyword to promote products, website or services. There are a lot of keywords searched by people all over the world. We have to get a specific keyword to our products/websites in order not to waste our adwords click on irrelevant visitor.

Some of the tools that we can use to get most searched keywords are from

There are some other commonly used site/tools to get the keywords. But those are the most popular ones.