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.
copay copy cop cowpea coop cope coup cuppa goopy coypu coupe cuppy koppa cowpie coypou cap cup kop cape capo gapy goop kapa
copay pay dopy dopa soupy soapy ropy ropey repay poppy poppa opah mopey mopy loppy loopy koppa goopy copy hoppy roupy soppy spay dopey choppy