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.
copra coppra coprah coper copperah cooper copier copper coppery coopery capoeira coappear caper capper cupper cuppier goopier kouprey
copra cooper whipray doper spray roper moper loper looper coprah coppra coper hoper para hooper aporia proa pray prau prao opera sopor supra toper whooper
cop coop copay cope copy coup coupe cowpea cowpie coypou coypu scop scope