This morning I was trying to remember the words to "Jesus Loves Me, This I Know." I've sung this song my entire life, and I couldn't remember the words for anything, so I looked them up. Now it's burned in my brain.
In the Red Dwarf episode "Tikka to Ride" there's a little ditty that Lister and Kryten hum as they walk down a corridor. That one has also been burned into my brain. I'd post a link, but the only links available are to the whole episode.