Dishonored at their local GameStop between now and January 27 will receive a code for "Dunwall City Trials" at no extra charge. Dishonored publisher Bethesda also notes the retailer will include the official game guide from Brady Games. The offer is only valid in-store for PC, PS3 and Xbox 360 versions of the game.
We now feel obligated to point out that the game is $52 on Amazon, so even with the $5 "Dunwall City Trials" included at GameStop, the math isn't that great for consoles (oh, the game guide? Here). On PC, the game was just $30 during the Steam Holiday sale, so you'll probably get a similar deal the next time another sale happens. Since this is Steam we're talking about, um, let's say sometime in the next month. Perhaps some clockwork heart and Valentine's Day tie-in?
However, if you've got plenty of GameStop credit just sitting around, one of the best games of 2012 is definitely worth spending it on.