If you start typing search terms into Firefox's Google search field, or if you use Google Suggest, Google taps into its knowledge of all searches and tries to guess what you're going to search for.
And if you type in just a single letter, you can really see an interesting slice of our searchable world: the most popular Google searches that start with that letter of the alphabet. Under the most popular one, you will see the others, in order by popularity:
If you don't recognize some of these sites, check them out. Lots of people appear to think that they're worth searching for.
"Kelly Blue Book" [actually "Kelley"]
"next" [could be the movie, not sure]
"U Tube" [see YouTube]
X Tube [WARNING: Adult content, NSFW]
Some of these suggested searches aren't for a particular site. They're just a search that many people make, and there's no particular site that is more popular than that search. In other words, there's no "killer" site or application that starts with that letter ... yet.