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.
spruce sprucy sprues spores sprees superrace spares sparse spires spireas spurries spiraeas suppress saporous spurreys spurious spurs spars sapphires sapors cypres spiers speers cyprus spoors spears sprays speirs sopors supers cypress sapours sappers sippers soapers suppers sparrows sporozoa
spruce peruse pierce price pursue caprice reprice repursue sprucy sprues superrace
sprue spirea supra spare sparrow sparry spiraea spire spar spore spiry spray spree spry spur spurrey spurry osprey