I'm a K.I.S.S. kinda brewer, so I have to go with the previously mentioned Thermapen. People who are struggling with their fifth or sixth cheap thermometer have no idea what they're missing.
Second place winner is a tie: Vinator or Fermtech autosiphon.
“Malt does more than Milton can / To justify God’s ways to man”
-A. E. Housman (1859–1936). A Shropshire Lad , 1896.