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.
whopper whapper whipper whooper whippier wiper weeper weepier whipray
hopper lopper bopper popper topper mopper shopper whopper copper chopper rapper sappier paper mopery soaper lipper loppier nippier cooper foppery happier gypper popery zapper ripper napper coopery coppra zipper supper doper tippier gappier choppier chippier nappier whippier whapper sipper wrapper dipper tapper quippier ropier zippier cupper zappier ropery gipper loopier reappear peppier nipper hooper hipper capper roper mapper coappear peppery soppier sapper pepper coppery quipper hippier piper moper kipper hepper looper dapper knapper goopier dopier opera tipper appear cuppier lapper copier mopier hoper dippier coper hoppier pappier loper toper upper whipper whooper chipper lippier shipper yapper per
whop whippy whoop whoopee whoopie wop