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