1. Google Keyword Tool (Free)
最大众化而且免费，深受广大群众欢迎。
http://adwords.google.com/select/KeywordToolExternal
2. KeywordSpy.com (Paid $89.95 a month)
http://www.keywordspy.com
3. Good Keywords (Free and Paid version)
http://www.goodkeywords.com
4. Traffic Travis (Free and Paid Version)
http://www.traffictravis.com
5. SEO Book Keyword Suggestion Tool (Free)
http://tools.seobook.com/keyword-tools/seobook/
6.KeywordDiscovery.com ($49.95 per month)
http://www.keyworddiscovery.com
7. WordPot.com (Free and Paid Version)
http://www.wordpot.com
8. Wordtracker.com
http://www.wordtracker.com
9. KeywordElite.com ($174 one-time cost)
http://www.keywordelite.com
10. KWBrowse.com (Free)
http://www.kwbrowse.com
11. Quintura.com (Free)
http://www.quintura.com
12. SpyFu.com (Free and Paid version)
http://www.spyfu.com
13. WordButler (Free trial then $19.95/month)
http://www.wordbutler.com
14. AdCenter Labs (Free)
http://adlab.msn.com
15. Nichebot.com
http://www.nichebot.com
16. Spacky.com (Free)
http://www.spacky.com
17. Google Insights (Free)
http://www.google.com/insights/search/
18. TheDowser.com (Free and Paid Version)
http://www.thedowser.com
19. KeywordExtend.com (Free)
http://www.keywordextend.com
20. GoRank (Free)
http://www.gorank.com/analyze.php
21. Trellian
http://ci.trellian.com/index.html
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