The smaller, the better. I got one of the Canon powershot models because my bigger camera is a Canon, and they use a similar menu system. So maybe one of the Nikon coolpix would be a good choice so you don't have to learn another system.

The other thing is the data card - get one with the same type as your other camera so you don't have to buy those all over again.

I think any of the current models of the major brands will take good pictures.