Lots of good responses here. I've got a .30-06 because my grandpa gave me one when I was 12, that's where it started for me. I've killed around 20 deer with it since then at ranges from about 15 yards to just under 400. I've shot paper out to 500 and currently do not plan on taking that particular rifle any farther, although it is certainly capable of it. I don't have the numbers that many here can claim, but I've killed deer with I *believe* 8 different cartridges. All those deer are equally dead. But when I get really serious about getting a deer on the ground, I always seem to grab the '06....it just seems like the right thing to do. As others have said.... If you could only have one rifle.... you wouldn't go wrong picking the .30-06.
-Jake