My son has this toy...of course it's Leapfrog (I should become their unofficial spokewoman or something;
. It's called the Phonics Desk. You put in a card, spell the word and there is a button to hear rhyming words. Just recently my son really got into this toy and loves the rhyming. It plays a little "rap" song and lists about 5-6 different words that rhyme for the word on the card.
I don't know if you can use this in your classroom, but you can certainly model it with rhyming songs and such. I think the hands on activities really help in this area. It's something that seems to be a little more difficult to explain in words and needs hands on things to accompany it.