through out history, i have heard of people taking a whitetail with a .22 long rifle. a well placed shot will take down anything permitted you are with in range.
with that said, i started out hunting whitetails with a .243.. not too bad, but i got far more kills faster with less tracking as soon as i went to a .30-06, and honestly, even more yet when i switched to a .308
today, I have four deer guns.. and i love them all:
modern day winchester model 94 .30-30 (for in the brush)
Remington model 700 BDL in .30-06 (for more or less everything)
Browning A-bolt stalker in .308 (favorite gun)
Tikka T3 hunter in 7mm rem. mag. (for hunting on the power lines and open fields)
if i cant take.... anything in north america with one of those four, really, i dont belong out in the woods.
a .223 will do the job, not recommended, but legal in many states to do so. i wouldnt, but thats me. .243 for me would be a very minimum.
the .25-06, .260, and calibers like that are better suited for white tails.
they are considered "varmints" in their literal sense, but they are BIG varmints. they are not woodchucks, ground hogs, or prairie dogs. they are many times bigger.