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.
loopier looper loppier loper lopper lippier leper lapper leaper lipper
copier dopier ropier goopier loopier mopier pier cooper hopper lippier pipier popper moper nippier hoppier loper mopper loppier roper soaper cuppier gappier sappier quippier soppier spier zippier hippier mopery opera peppier bopper popery choppier lopper happier coper chippier pappier hoper nappier tippier looper topper piper dippier hooper whooper doper coopery weepier rapier ropery roupier seepier soapier soupier zappier copper toper typier whippier whopper chopper shopper per