Finding Great Keywords

OVERTURE
Overture has a keyword suggestion tool: Just type a keyword in and it gives you a list of keywords that are related to yours ranked in order of how many people searched for the
Keyword on the Internet.
Overture Keyword Suggestion Tool

ADWORDS
Adwords has a tool for people who advertise on Google. The tool helps them to find additional keywords to bid on that are related to the main keyword they are bidding on.
http://adwords.google.com

WORDTRACKER
Wordtracker is generally considered the best available resource for keyword analysis for web site promotion. However, it does come at a price, whereas the others are FREE.
http://www.wordtracker.com/

NICHEBOT
http://www.nichebot.com/

NICHE KEYWORD TOOL
Niche Keyword Tool