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.
soppy soapy soupy sappy spy sop spay soup soap sepoy zippy seepy zappy hyssop sap sip spa sup seep sipe spae spew spue supe
loppy poppy hoppy choppy soppy lippy dopey zippy soupy sappy koppa soapy ropey guppy goopy tippy nappy gappy mopey loopy chippy shoppe pipy poppa ropy dopy peppy dippy zappy copay puppy pappy whippy nippy roupy copy mopy buppy happy hippy cuppy quippy yuppy