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.
pipiest pappiest peppiest papist
hippiest zappiest zippiest loopiest hoppiest mopiest cuppiest tippiest nappiest weepiest peppiest happiest quippiest sappiest dopiest whippiest chippiest seepiest typiest ropiest dippiest roupiest soapiest pappiest goopiest choppiest gappiest pipiest soppiest lippiest nippiest soupiest loppiest pest pesto deepest piste heppest ripest typeset rapist typist papist pesty cheapest sapphist hippest pst