http://tools.seobook.com/keyword-list/generator.php

This tool is for AdWords users, but since AdSense publishers are often Adwords users themselves, this will do. This is a free open source keyword phrase list generator, you can write a list of keywords in separate boxes and it will generate a list of keywords (keyphrases) for example:
box 1: buy, order, purchase
box 2: apple, orange
box 3: cheap, best

it will generate for you keyphrases like these:
buy apple cheap
buy orange best
order apple best

etc, etc.

You understand? That’s the tool you want to generate big lists of keywords, that’s the only way you can succeed with Adwords. Now you can use this online version for free or download the open source script and install it on your webserver!

http://tools.seobook.com/keyword-list/generator.php