Like someone else posted -- the actual temperature could really make a difference between the doctor's office saying "treat at home," "bring him in today" and "get him to the hospital, now." It's pretty serious to us -- but our pediatrician has written articles about fever in kids and has always been a stickler for wanting accurate readings. (She wouldn't be keen on the idea of "I can tell by feeling the forehead!" You can't tell by touch if it's 100 or 102 or 105 that way, and there is a huge difference in a kid -- the latter would be cause for serious and immediate intervention.) When our girl was little we did use rectal temps; our doctor always said they are really, truly the most accurate in infants and toddlers and are NOT "traumatic" as someone posted -- not if your child is used to it and the parent does not get all wound up and upset about doing it. I think most parents just feel like it's invasive, and it is, but doctors wouldn't hesitate to do it. As kids get older, oral is the way to go. I don't like the forehead readers, myself, as I feel they are not going to give me a real temperature, only some "range" indicated by a muddy color I can't really determine. So...for little ones, rectal, done with the right thermometer, KY jelly and thermometer covers, and plenty of distraction for the little one during the process; and for older kids, a good digital oral thermometer (with covers, again) and pratice at keeping it at the "root" of the tongue.
Ear thermometers -- had one, she hated the feel of it and wiggled, and thus I never trusted the readings. Some parents have very good ones that cost a lot and those are supposedly OK, but our experience with one was pretty poor.