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.
aspire asper
spire respire aspire suspire speir waspier spare despair spirea spiry raspier oospore zappier sprue spree spore zippier soapier seepier sappier spier osprey sapphire zoospore soupier diaspore soppier wispier