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.
proper propria preppier puerpera puerperae puerperia prepare purpura purpure
roper trooper groper proper wrapper rapper creeper sirupier dorper harper frippery ripper croupier crepier carper chirpier warper crapper tripper grapery roupier ropery ropier griper larruper dropper drippier drapery grouper gripper reappear rapier gripier riper grippier crappier creepier cropper crupper grapier chirper reaper trouper preppier raper puerpera syrupier draper dripper droopier trapper trippier sharper
prop perp preop prep prepay preppie preppy pyrope