- KeywordEye - keywordeye.co.uk - Free version has limit of 100 keywords, and sorting of cloud visualization by Adwords competition or search volume.
- KeywordSpy - www.keywordspy.com - Key feature is domain spy tool, which allows you to type in a domain and get data on how much money they're spending on paid search, a list of competitors, and what they're paying for individual keywords.
- SEMRush - www.semrush.com - In one view, you can see how many search results for that keyword (indicating competition), and points out some words to put into the negatives of your PPC campaign
From the article:
One of the hardest things to do in keyword research is to uncover related keywords. With that in mind, the tools I’m reviewing today all help identify related keywords that you may want to search in more detail. These tools are not a substitute for detailed keyword research like I talked about in...