I'd like to get the Dungeon Keeper games, as I know the second one is fun (I had it, but it was buggy on the system I owned). They're on sale now, but I have to make my wife's present a priority. Last minute, we decided to get eachother presents and I'm low on cash as it is.
I can highly recommend Dungeon Keeper 2. It was lots of amusing fun :)
I've not played them, yet! They're high on my backlog though.