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