The most recent and so far, most permanent (in the sense that it's been a month since it happened and he hasn't immediately come back to life) demise that the Dark Knight has suffered came in the pages of Scott Snyder and Greg Capullo's Endgame. The storyline in the main Batman title saw the hero facing off against his arch nemesis for what seemed like the final time. Riffing on their brutal confrontation in Fran Miller's The Dark Knight Returns which turned fatal for one of them the climax of Endgame saw the Clown Prince Of Crime and Caped Crusader fighting in a series of underground caves which housed a hidden pool of life elixir stuff that previously brought The Joker back to life. Not particularly wanting the most dangerous man in Gotham to be essentially immortal, Batman pulled out all the stops to first cease a city-wide dosing of Joker venom and then to off the bad guy himself, once and for all. There was eye-gouging, back-stabbing, and finally the two of them collapsed in a heap of limbs and blood, with the cave then caving in on the both of them.
Tom Baker is the Comics Editor at WhatCulture! He's heard all the Doctor Who jokes, but not many about Randall and Hopkirk. He also blogs at http://communibearsilostate.wordpress.com/