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