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.
soapier soaper sappier soppier soupier spier sapper zappier seepier sapor speer spire sapphire speir sopor spiry super sipper zapper sapour spirea supper zippier spiraea spry spur spar spear spoor spree sprue spare spore sparry spurry zipper spurrey
rapier soapier pier aper gawper apery piper hoppier pauper nippier weepier happier chippier soppier napper knapper mapper raper rapper loopier spier heaper soaper yauper shaper whippier ropier wrapper sappier dapper tippier hippier leaper zappier diapir dopier tapir nappier papery paper cheaper quippier cuppier pipier peppier gaper lippier gappier typier caper lapper loppier mopier copier japery goopier napery soupier tapper taper dippier diaper zapper reaper zippier japer pappier seepier sapper roupier whapper choppier yapper capper yawper per