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.
whapper whipper whopper whippier whooper wiper weeper weepier whipray
capper yapper zapper knapper lapper tapper whapper mapper dapper wrapper rapper napper sapper aper hippier ripper gappier sipper cupper sappier pepper heaper copper raper lopper upper hopper nippier foppery mopper lipper dipper dippier apery tippier yauper shopper shaper chopper chipper whopper whipper zippier reappear lippier zipper nipper hoppier zappier caper gawper leaper peppier diaper piper rapier happier bopper soaper quippier taper reaper japer cuppier popper japery nappier gipper hipper peppery pauper gaper quipper coppery coappear kipper topper appear pappier supper soapier soppier napery tipper paper loppier papery gypper whippier cheaper chippier choppier shipper hepper yawper per