I still remember, as a child, playing C-E-G-B and thinking how discordant it sounds. Now a Maj7 is an essential part of much of my output.
Other examples include microtones/non-equal temperament, odd time signatures, and the aspect of rhythm being off-"true" (swing, Brazilian, Balkan, Viennese Waltz) - is there a good name for that last one?
Cheers, Mike.