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