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.
nappy nappe nappa nippy nap nappie knap napa nape neap nip knop neep nipa nope
happy nappy pappy sappy gappy zappy app peppy hoppy dippy hippy gapy buppy nappe kappa tippy poppy soppy choppy quippy chippy heapy whippy nippy guppy pipy teapoy cuppy pappi loppy puppy soapy zippy nappa lippy yuppy