Pay Per Click Tools
WordTracker -Data is based on the Metacrawler and Overture search engines.
KeywordDiscovery - Data is based on the number of search engines.
Keyword Optimizer - Enter a list of keywords and this tool will remove any duplicate entries and re-order the list alphabetically.
Google Analytics - Provides deep analysis on all traffic, including paid search.
Google Suggest - As you type, Google provides the top 10 most popular keywords that begin with the keyed-in letters, in order of popularity.
SpyFu - Find out what competitors are biding on and estimates for the cost of PPC advertising and others bells and whistles.
Hittail – Finds and easily groups the actual terms being used to find your site into an excel format. Great for finding niches
and long keyword strings.
Google Trends - Graphs historical trends of various Google searches.
Google Keyword Tool External -Historical trends in keyword popularity.
BidCenter - A good tool for comparative analysis and easy to use
SEO Sleuth - Find what AOL users search for (AOL produces 2x the retail conversions as any other engine)
ROI Calculator - This calculator measures the ROI (return on investment) of a CPC (cost per click) campaign