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