Super Mario Galaxy, Deus Ex: Human Revolution, Skyward Sword and Borderlands 2. I love cases that have nice designs, they appeal to me a lot. Super Mario Galaxy is such a beautiful case, the text, the design, all so pretty! Borderlands 2 is another game which doesn't lack in either of those departments, the case was very well made. Deus Ex, just because it looks epic. The colors work really well and the amount of detail that has been put into it is amazing if you look fairly closely at the case. Skyward Sword, though, is astonishing. I adore the case so much, it just looks so good and everything is right with it, cannot complain one bit about it imo.
In general, I love seeing good box art. I put the best cases on display resting against my pile of games because they make it look nicer. When I buy a game, box art can sometimes help with the decision on whether to buy a game or not, it's important to me :3