[Steve]

For the cost difference you are better buying the fastest you can as when you change your camera again (very likely) it will be able to take advantage of the faster speeds of the cards to make use of the bigger burst speeds.

Unless your daughter has the cards away, its likely that whatever you buy now should last for longer than your current cameras and memory has never been as cheap.

Edit..I have several Sandisk Ultra II cards but my recent additions have been 4GB ultra III's. Its worth noting though that the 1gb Sandisks (from whatever range) are faster than the 2/4/8gb versions of the same range. So if absolute speed is needed then buy more of the 1gb versions