Penny has a favorite toy that makes a crinkly noise. When it fell apart because we play tug-of-war with it (which we know is a silly thing to do with a soft toy), I decided to sew it up because she loves in so much. To my surprise I discovered that the weird noise is just an ordinary plastic drink bottle inside it.
Therefore I was excited to read on The Pet Haven blog that there is a company that sells soft toy casings that you can put onto a plastic bottle. I had a look around the Net and found that FatCat Inc.com sells them. They look great, obviously not for tough chewers, though.