Post 29:
There are a couple ways to answer that question. First - the strongest keywords for you personally are the ones that are related to what you are selling or specializing in. If you sell Blackberry Cell Phones, thats your most important keyword and you should optimize for it. Those keywords should be repeated throughout the page.
If you are looking for popular keywords in general, eBay has
Link which shows whats popular on eBay and Yahoo has
Link which shows the most searched terms on Yahoo.