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.
sapphire sappier spire spirea sapper soppier zappier spiraea soapier sprue spare speir spiry sapor spree spier spore sapour zapper sipper soaper supper soupier zippier spurrey seepier spry spur spar spear speer spoor super sopor sparry spurry zipper