WebmasterWorld member Receptional Andy suggests the unconventional way to perform keyword research: offline with two books.
The first book is the useful dictionary. If you do a search for "widget," for example, you may get an origin phrase, and in this case, it's "gadget."
The second book is the related reading guide: the thesaurus. You can get plenty of comparable words by using the thesaurus.
Then, you just need to write down everything on paper. No need for a computer at all.
Now I'm not sure how many people will do this, but the idea is an interesting one. :)
In fact, as one more modern member suggests, the idea of keyword research is to get information of what people are actually searching for. That said, the oldschool traditional killed-trees version just doesn't cut it.
Still, as Andy responds, some keyword research tools aren't helpful, and using a dictionary and thesaurus may add some words that you may otherwise not have thought of.
Forum discussion continues at WebmasterWorld.