Because according to Amit Singhal, principal scientist at Google, a guy who really should know what he's talking about, over 50% of the 200 million searches performed a day have never been searched before. He also said: "When performing a search most surfers give a 2-4 word query".

So here are my top 18 recommended ways to build massive keyword lists:

1. Visit your competitor's web pages and look in the title and meta tags.

2. Search for brand names in Google's Sandbox. This will return additional keywords that searchers entered when using the brand name. You can also enter regular keyword phrases and get related keyword phrases that have been searched on Google. Link: https://adwords.google.com/select/main?cmd=KeywordSandbox

3. Look over your past customer testimonials, and see if there are any keywords you can use. This strategy lets you get inside your customer's mind to produce more market centric keywords.

4. Consider synonyms. A synonym is a word having the same or nearly the same meaning as another word or other words in the language. Enter your keywords into Roget's Theasaurus for a list of related synonyms. Also visit LexFN. Links: http://thesaurus.reference.com & http://www.lexfn.com

5. Think of singular and plurals keywords.

6. What about verbs? Example: Ride, rode, ridden, ridding, rides.

7. Use hyphenation and variations. Example: off-shore, offshore, off shore.

8. Consider domain names. Many people enter domain names into the search engines rather than their browser address bar. Example: cnn.com. In June 2005 cnn.com was searched 843,256 times on Overture.com.

9. Get books on your subject and use the terms in the index and glossaries to grow your keyword lists.

10. Download a free copy of Weblog Expert Lite. Then ask your web host how to download your raw stats files. Run them through the software and you will then discover every possible keyword combination that surfers have used to find your website. Link: http://www.megastep.com/wle

11. Use Wordtracker. What does Wordtracker do? "... helps you find all keyword combinations that bear any relation to your business or service - many of which you might never have considered." Wordtracker is an essential tool to use. Link: http://www.keywordlistbuilder.co.uk

12. Then go to the Overture Keyword Suggestion Tool. Enter in a keyword and Overture returns all the prior month's searches that include your phrase. The problem with the Overture tool is that it doesn't give you the exact way that the search was entered. This is why it is essential to use a tool like Keyword Tumbler (see # 18) to generate the maximum possible number of keyword combinations that a user might enter a search phrase into the engines. Link: http://inventory.overture.com

13. Use abbreviations and misspellings. A good misspelling tool is Search Spell. Search Spell uses actual misspellings entered into the search engines. Misspelled Keywords is another software tool that will literally create thousands of misspellings for any given keyword phrase you enter into it.

Link: http://www.searchspell.com/typo & http://www.misspelledkeywords.co.uk

14. Use acronyms. An acronym is a word formed from the initial letters of a name. Example: due diligence becomes DD. A good acronym generator is Acronym Finder.

Link: http://www.acronymfinder.com

15. Combine your keyword phrase into one word. Example: strawbale houses => strawbalehouses.

16. Use "space" and "+" with keywords. Example:

- strawbale+houses

- strawbale +houses

17. Visit Crossword Compiler and download their demo software. Plug in your keywords and discover a multitude of additional words. Link: http://www.crossword-compiler.com

18. Once you have your list compiled visit Keyword Tumbler and download the free software. Put your keywords into a text file and then let Keyword Tumbler generate multiple variations of each keyword phrase you have... instantly! Link: http://www.keywordtumbler.com

It does this simply by mixing the words in each phrase around. Example: "horses for sale" generates a list like this...

horses for sale

horses sale for

for horses sale

for sale horses

sale horses for

sale for horses

As Perry Marshall, author of the Definitive Guide to Google AdWords said at a recent seminar: "Every combination of keywords that somebody could conceivably type in on Google is a market."

Link: http://www.megastep.com/pm

I hope you have found this advice useful? It's the exact same procedure I use everyday when fighting the pay-per-click wars.