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.
openness opens opines
openness loopiness cheapness dopiness dippiness spinnies soppiness sappiness ripeness pipiness peppiness nippiness nappiness mopiness lippiness pannes hippiness hippieness hipness happiness pinnies pennies ropiness soapiness spinneys deepness dopeyness weepiness choppiness