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.
puppy peppy pappy poppy pup pupu pipy pupa pupae poppa pappi pop pap pip pep papa peep pepo pipe poop pope
buppy guppy yuppy puppy cuppy cuppa chuppa quippy chippy poppy tippy happy zippy hippy soupy hoppy sappy gappy pipy loppy lippy soppy nappy zappy nippy dippy pappy whippy peppy choppy roupy
puppy pup yuppie buppie buppy huppah cuppa cuppy guppy pappy pappi peppy poppa poppy pupa pupae pupu yuppy