I like the Saboteur box art for starters. It has a very distinct graphic art style to it.
Box art in general is the equivalent of marketing; for many consumers, that shelf presence may be the only bit of marketing effort that influences whether they even look at a game or not.
For titles with a good marketing effort behind it, or a title that was generally known about well in advance, bad cover art won't kill sales. Think Street Fighter II for the SNES/Genesis or Super Street Fighter II, both of which had some of the worst cover art of all time, yet broke sales records.
Generally speaking it will only be the walk in customer with no prior knowledge of a given title who will be influenced either positively or negatively by cover art. So in a way, it can hurt sales of lower profile games.
