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.
speer spree super spier speir spear sipper supper soaper sapper spur soupier spry seepier soapier soppier sappier spar supra spore sopor sprue spire spoor spray spiry sapor spare zipper zapper spurry spirea sparry sapour sparrow spiraea spurrey zappier zippier sapphire
peer speer per hoper napery lapper capper happier nippier loopier gaper gawper lopper pear peery coppery hoppier mapper copper quipper cooper seepier nappier pappier peeper peri hepper mopper piper cupper pere coper keeper hyper popery mopery japery ripper pier leper tipper whapper typier doper chipper cheaper weeper taper whippier speir chopper shaper shopper whopper yauper deeper supper raper zippier hippier spear toper roupier peppery reappear soppier zappier lippier rapper dipper ropery duper sapper soaper spree paper gypper popper upper dupery apery tippier dapper beeper hooper shipper dippier zapper pauper japer goopier appear chippier aper spier papery roper bopper hipper ropier leaper caper whipper cuppier loppier lipper viper nipper hopper mopier quippier coappear wiper super foppery napper coopery gappier reaper looper gipper copier knapper pipier kipper pepper moper loper opera heaper peppier sappier yapper diaper choppier weepier topper tapper dopier zipper pree wrapper whooper soupier riper soapier sipper rapier cheeper yawper
seep seepy sipe spae spew spue supe