The 30-06 has seemingly become the workhorse whitetail caliber these days.  Used to be the .30-30 in Grandpa's day.  Some people really dig the .270 and of course the .300 is a staple for those who don't mind a good whallup to the shoulder.  I've got a good friend that wouldn't dream of hunting without his 7mm.  The .243 is popular for youth hunters and has plenty of firepower if the shot is placed correctly.  A lighter kick makes placing a good shot much easier.  The .45-70 was the premiere caliber for deer hunters in the late 1800s.  It's still a nice gun for shooting deer at close range.  There are many more out there.

What is your whitetail medicine of choice?