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