Setting Up Campaign Seeker Keywords
Google Keyword Tool https://adwords.google.com/select/KeywordToolExternal
Spacky http://www.spacky.com
Free WordTracker http://freekeywords.wordtracker.com
SEObook http://tools.seobook.com/keyword-tools/seobook/
SEOChat http://www.seochat.com
KWBrowse http://kwbrowse.com
Wordpot (Daily search prediction) http://www.wordpot.com
Keyword Discovery. http://www.keyworddiscovery.com/search.html
Keyword Country http://www.keywordcountry.com/free-keyword-tool/
Google Traffic Estimator https://adwords.google.com/select/TrafficEstimatorSandbox
Google Search-based Keyword Tool http://google.com/sktool/

Spy Tools
SpyFu http://www.SpyFu.com
KeyCompete http://www.keycompete.com/home.asp
KeywordSpy http://keywordspy.com/
HexaTrack http://www.hexatrack.com/home.php
Wordze (Not Free) http://www.wordze.com/
ISpionage (Not Free) http://www.ispionage.com
PPCKahuna (Not Free) http://www.ppckahuna.com
NicheBot (Not Free) http://nichebot.com

Synonyms & Themed & Relative
MSN http://www.msn.com
Ask (“related searches”) http://www.ask.com
Clusty http://clusty.com/
Quintura (“related themes”) http://www.quintura.com/
Thesaurus http://thesaurus.reference.com/
Synonym http://synonym.com/synonyms/
Synonymlab http://www.synonymlab.com
Google Insights http://www.google.com/insights/search
StrategicProfits http://www.strategicprofits.com/visualwords/

Demographics
Alexa http://www.alexa.com/
Quantcast http://www.Quantcast.com/
Plenty Of Fish http://www.plentyoffish.com/demographicInterests.aspx

Niche Investigation
Google Trends http://www.google.com/trends
Yahoo Buzz http://buzz.yahoo.com/
Ask Top Searches http://sp.ask.com/en/docs/iq/iq.shtml
Amazon http://www.Amazon.com/  
Ebay Pulse http://pulse.ebay.com
Ebay Reviews http://reviews.ebay.com/
Ebay Popular http://popular.ebay.com/
Wordtracker Gtrends http://freekeywords.wordtracker.com/gtrends/

Headline/ Ad research
Google Ad Targeting Preview https://adwords.google.com/select/AdTargetingPreviewTool
Digg (See Headlines) http://Digg.com
Popurls http://popurls.com/
AmInstitute http://www.aminstitute.com/headline/index.htm

Miscellaneous

http://conversion.7search.com/scripts/advertisertools/keywordsuggestion.aspx

http://www.offervault.com

http://labs.ebay.com

http://affspy.com/beta

http://adlab.msn.com/Keyword-Group-Detection/

http://lycos.top50

https://www.google.com/adplanner

http://semrush.com

http://www.nicheprofitclassroom.com/keywordTool.html

http://technorati.com/pop

http://delicious.com/popular

http://www.shopping.com/top_searches

http://www.seomoz.org/popular-searches/