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.
cooperate coopered coppered coappeared capered cuprite copyread kippered
cooperate operate reoperate prate pirate yperite biopirate separate suppurate depurate uprate pert prat
cooper coopery coper copier copper copperah coppery scooper