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.
coappear capper copper coppery caper coper copperah copier cupper cooper coppra coopery gappier cuppier capoeira gaper gawper kipper goopier quipper quippier copra coprah keeper
appear coappear reappear pear bopper mopper pepper loppier paper lippier whipper hopper chippier nipper hipper quipper napper peppier tippier lapper wrapper foppery hippier shopper choppier whopper upper popper hepper sappier tapper copper soppier supper zappier zippier dipper happier capper coppery gipper topper pappier kipper cuppier gypper hoppier lipper rapper whippier lopper nappier mapper nippier knapper quippier chopper gappier sapper tipper dippier dapper zipper zapper spear cupper sipper ripper piper peppery whapper chipper shipper yapper par per