PPC Keyword Research Tools

KeywordDiscovery - Advanced keyword research tool and pay per click keyword suggestion tool.
WordTracker: WordTracker provides new keyword ideas; helpful for brainstorming and discovering new keyword ideas.
Google Keyword Generator: This free keyword suggestion tool generates keywords suggested by Google for a given search term.
Keyword Geo Targeting and Wrapping Tool: Add city, state, and/or zip codes your keyword list, and then choose how to wrap them with this Geo Targeting Keyword Tool
Overture-Keyword Selector Tool: Not sure what search terms to bid on? Enter a term related to your site and Keyword Selector Tool will show you.
Combine Words: Use this pay per click tool to create combinations of keywords for use in a Google AdWords, Yahoo! Search Marketing, adCenter or Ask.com Pay Per Click PPC campaign.
Microsoft adCenter Labs: Microsoft adCenter Labs is dedicated to developing cutting-edge new ways for consumers and advertisers to connect - on of which is the Ad Text Writer which Automatically generates text ads for a given URL.
7Search: This ppc keyword research tool utilizes data based on 7search.com to assist with keyword expansion.
Miva: Based on Miva search data, use this keyword research tool to find not only how many searches that keyword has received in the past 30 days, but also additional related searches that include your keyword.