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.
flopper floppier flapper flipper flappier
lopper flopper sloppier slippier slipper gloppier clipper lapper lipper lippier looper loopier loper blooper loppier eloper flapper flappier flipper floppier clapper galloper slapper slippery sloper walloper