If you need to procrastinate but still want to (pretend that you) do something of educational value, I recommend the “Great Language Game”. You listen to short clips and have to identify the language of the recording. At first you must choose between two different languages, but as the game progresses you get offered up to six choices, making it harder to get it right merely by luck. You get 50 points for each correct answer and the game is over after three mistakes.
My score was 750 points, putting me in the top 10% according to the current statistics.
Some of the choices were really simple for me, like the one between German (my mother tongue) and Yiddish, or picking Italian, a language I am currently learning in anticipation of my move to Italy next month. Also, Slavic languages were easy to identify if all the other choices were non-Slavic. Because it sounded very much like a Romance language, I was able to identify Romanian, although I had never heard it before.
With other languages, I was just lucky in guessing them right.
My three mistakes? I confused Khmer with Tagalog, Sinhalese with Thai and Welsh with Scottish Gaelic.
(Hat tip to Crooked Timber, where I found the link to the “Great Language Game”.)