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.
coop cop coup goop copy cope coypu goopy coupe copay cowpea coypou cowpie cap cup kop cape capo cuppa cuppy koppa
hoop coop goop loop poop whoop op
coo cooee cooey coocoo cook cookey cookie cooky