I've taken a list of English words, and examined each of them to see what they sound like (using the PHP metaphone function). This page lists the most common metaphone codes, along with their words. You can also search for a word of your own, and see which words sound similar - and which ones rhyme, and which ones alliterate.
cup coup cuppy cuppa coupe cap cop copy quip coop cope capo cape copay coypu guppy quipu cowpea cowpie coypou quippu quippy