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.
spense speans spence sapiens spinose spins spans sapience spawns spines spoons spinous supines sapiency spinneys spinnies spooneys spoonies sappiness soapiness soppiness
spense paeons cheapens deepens pensee speans sapience ripens peans peens peins pence penes penis pens paeans peons happens copens lippens opens reopens ripienos sapiens spence spinose tuppence shippens
span spean spin spine spinney spinny spiny spun aspen