Those people over at Google have just released a Beta version of their Google Suggest. This is just like normal Google, except that as you type it guesses what you’re trying to search for based on the most popular previous searches.
On a related note, over at WordCount.org you can see what the 88,000ish most popular words are in the world – interactively. And you can search for your favourite words. But whilst you’re searching, QueryCount is watching you and updating the list accordingly. Go search for something unusual and skew the results 🙂