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