I personally love these. There called Terramundi pots you can get them personalised or with different colours and writing. When they're full you smash them and spend the money. See link below.
I'm with Spannet in this one...i've bought Terramundi's for two of my friends babies and both absolutely loved them. They come with a little wish slip too, which you fill in then slip into the pot.
The Disney Shop do lovely ones, my daughter was given one last year and she loves it, it is winnie the pooh eating a pot of honey, and is made of china. I think it was about �20 but is really lovely especially if you are fan of winnie the pooh!!
One that you need to smash to get the money out of may be alright be for someone older, or whilst she's a baby, but my children always loved emptying out their piggy banks and counting the money to see how much they'd saved up. I saw some lovely money boxes in John Lewis today, all kinds of animals, I think my favourite was the hen!