The post of the day, I know it is early still, is at WebmasterWorld.
Everyone knows how to add a suffix or use a thesaurus, but that is only the beginning. How do we find words that Google knows relate to our target term?
Currently, the tilde search operator is my weapon of choice. Let's see if Google sees any relationships for the ubiquitous widget. Notice that GUI is bolded in the SERPs. We now know Google sees a relationship between those two words. In theory, including GUI on your widgets page will increase your ranking for widget but not vice versa.
Too find all of the terms related to widget, we could simply browse the listings looking for bolded terms. But I'm too lazy for that, so I begin excluding words from my query, starting w/ my main term. Be sure to collect all your traditional stemmed words( widgeters, widgeting, etc) before excluding your main search term. Each new match is added to my exclusions until no results are found. You end up w/ a nice list of related words that can be copied out of the search box.
One downside to this strategy is the chance of missing out on potential matches that only appear on pages you've excluded from your search. However, the time savings is worth it when working with thousands of pages.
Give it a go with a less generic term, and you'll begin to see how much more natural "keyword stuffing" can look now. Anybody else working on a personal Google thesaurus?