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.
sap soap sappy soapy spy spa zap sop sip sup soup seep spue spew sipe spay spae supe seepy sepia sepoy soppy soupy zappy hyssop