Hard shell, lots of beef (a good chilli con carne or something), cheese, lettuce and diced tomato (perhaps the only time I actually prefer tomato on my food without it being a sauce). Oh, and salsa, of course. That'll do me. And the hard shell is important... for me, if it's not cracking apart in your hands and making a mess, it's not a proper taco experience. Just the way I was brought up, I guess.