Most of the Neighbourhood, Rock, Jazz tracks from the base game, the Disco tracks from House Party, and the neighborhood tracks from all subsequent expansion tracks.
If you've played The Sims without any expansion packsnote and have the American version of the game, chances are you'll recognize Neighborhood 1, the first song that plays every time you enter the neighborhood screen for the first time. Also a potential Ear Worm, this jazzy tune lovably conjures up imagery of 1960s and 1970s suburbia.
Pretty much all the real life songs played on the radio are excellently chosen, but many consider this, played on the College Rock channel, to be the best one by far. They actually got the real singers to do their song in SIMLISH.
W of P3 - Aff Wubbas Doo. Unfortunately, it was created just for Sims 2 Pets, but it's unlikely you'll ever hear it if you don't also have University.