"Pursuit of Happiness" is the kind of generation-defining song that simply never gets old. Rapper Kid Cudi (Jan. 30) changed the entire music scene with his 2009 debut album Man on the Moon: End of the Day, and influenced all kinds of artists after him. Showing people the power of positivity even through the most difficult of circumstances, songs like "Pursuit of Happiness" and "Day 'n' Night" will forever be classics.