Plus, there's the one with A Christmas Story re-imagined as a horror film. That's pretty funny. I also like the X-Men: Last Stand / Office Space one as well. It's interesting how some of the shots can be so dramatic when taken out of context. I may never look at Office Space the same way again. Well, I probably will. And, of course, the mash-up got even more popular thanks in large part to those two gay cowboys in Brokeback Mountain (as our own Martha rightly pointed out before). So you had a string of Brokeback mash-ups which now run into the dozens over at YouTube. Search, you'll fine 'em. My favorite -- Brokeback to the Future. Now that's what a mash-up is supposed to be.
There's even a website (probably more than one) devoted completely to mash-ups that you can check out if you feel strongly about your love for these things and just want more, more, more of them. Which brings us to one of the latest ones -- a mash-up of Apocalypto and The Last Kiss called Zach Brafs' Apocolypto. Not as funny as Brokeback to the Future but I give them an "A" for effort. Enjoy.