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.
whippiest weepiest
happiest hoppiest lippiest tippiest pappiest sappiest chippiest nippiest zippiest whippiest hippiest dippiest nappiest zappiest soppiest loppiest choppiest quippiest cuppiest gappiest peppiest mopiest hippest soapiest weepiest seepiest loopiest pipiest soupiest roupiest sapphist goopiest papist typiest heppest ropiest dopiest pest