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.
soupy soup soapy soppy sup sop spy supe soap spay sappy seepy sepoy hyssop sap sip spa seep sipe spae spew spue
roupy soupy choppy dopey soppy loppy soup soapy roup ropey poppy mopy mopey loupe loup loopy guppy hoppy goopy cuppy coupe coup copy copay puppy ropy buppy dopy yuppy