How about the Tantus Cush or Flurry? They have a nice filling girth and are made of 100% pure quality silicone, a great jump up from the Oh! Rabbit. They have a realistic shape too.
I honestly wouldn't touch anything other than silicone so I would suggest something from the Tantus range as suggested by HE. Here are some I've found...
I would highly recommend the Tatus Cush. I've wanted it for ages but I've been put of by the high price. I finally took the plunge and treated myself a couple of months ago and trust me, it was SO worth it. It's definitely in the top 5 of my favourite toys.
I've recently purchase this http://www.lovehoney.co.uk/product.cfm?p=8590 and it fills me up nicely and easy to use on others with it having a handle. Its great fun and certainly recommend it