[a work in progress]
Josh "Can Lift More Iron Than Should Be Legal" Rubin has a useful page outlining how to measure and what different values might suggest.
I've tried more thermometers than I'd like to admit (including all kinds of cheapo ones, the commonly-suggested Geratherm, and the well-reviewed Exergen temporal artery scanner), and I've finally found one that I harrass everyone I know to buy, the Braun Thermoscan 5 ear thermometer. I've found it more reliably-repeatable and convenient than any of the others, which makes it easy for me to stay consistent. They go pretty cheap on ebay if you get an open-box / used model. You just have to overcome the mental images that it might've already been used by these guys.