When I'm looking for the keywords to use I really go back to the basics...

FIrst one is to go to the Google Keyword Tool and simply put the same URL you are using for your display url into the tool and choose 'Website Content' and click go.

This will take a look at the site of the offer and grab what it thinks it is all about. Any of the keywords here that stick out as the sort of thing people looking to buy or try something out would use are great to put into your Yahoo acount, don't forget to check out the CPC but also remember that this is on Google and should be slightly cheaper on Yahoo... this isn't always the case but it is a good way to think... :)

I also pop the main keyword for the offer (eg Teeth Whitening) into the Google tool and choose 'Descriptive words...' and hit go. This will also throw out some great keywords to use. You will also find that it may throw up some angles you hadn't thought of that you can dig even deeper into... it's all about keeping an eye out for 'buyer' keywords that don't cost the earth!

Another great free keyword tool is the SEOBook one at http://tools.seobook.com/keyword-tools/seobook/ just put the main keyword in and it will give you some more keywords to add.

They are plenty of other ways to get some great keywords but again there are some awesome guides on that in WA so I'll leave that to them...

Now finally how about some tips on how to write an awesome advert for your PPC to CPA campaign....