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.
rapist ropiest rapacity roupiest repast ripest ripost reposit riposte rapeseed reposed repassed
rapist papist typist pst pest epeeist soppiest happiest goopiest sapphist ropiest loppiest dopiest past deepest zappiest typiest lippiest cuppiest hoppiest hippiest hippest heppest upset whippiest chippiest gappiest sappiest ripest psst nippiest pipiest roupiest ripost repast peppiest post mopiest loopiest seepiest nappiest bypast quippiest soapiest soupiest zippiest dippiest tippiest pappiest piste weepiest cheapest choppiest
rapes fraps trappous trapezii trapeze raps reaps rupiahs wraps frappes rappees crappies crapes craps grapes grappas drapes traipse trapes trapezia trappose traps