The balance between bass line, rhythm and melody is illustrated clearly in different styles of dance music. Styles with more syncopated drums (nu skool breaks, UK garage or drum and bass) tend to have the bass line as a very central element to the songs, with the other instruments often being designed to complement the bass rather than the other way around. In these styles, the bass line rather than the bass drum tends to provide the main 'kick' to the rhythm (some drum and bass tunes actually use a tuned 808 bass drum sample as the bass sound) Often, the bass sounds are distorted so that the harmonic content of the sound includes more high frequencies, leaving less space for other sounds in the mix. These techniques are flooding over more and more into pop music, especially R&B of the Timbaland / Neptunes / Missy Elliot variety. If that doesn't count as pop, how about Britney Spears? 'Baby One More Time' has a great rythmic bass line.

At the other end of the spectrum is music where the bass line is of the simple, off beat, matched to the chords variety. This is most obvious in commercial trance, music with a very simple rythmic element, where the chord structure and melody are more important. The bass sounds here tend to be simple and deep, with the higher frequencies filtered out. Once again there is a crossover in to pop music; Steps, Vengaboys and Aqua being obvious examples.

You could argue that dance music took these techniques from hip hop/funk and eighties europop respectively, but over the years, the demands of the dancefloor have honed the techniques to the point of maximum effect, the ideas taken to their logical conclusion. As the commercial trance disaster of 1999 (I'm speaking from a UK perspective here) proved, this is not always a good thing!

Top Bassline Records;
Azzido de Bass - Doom's Night (Timo Maas Remix)
Roni Size & Reprazent - Brown Paper Bag
Stanton Warriors - Da Virus
Daft Punk - Around the World
Buddy Rich (covered by All Seeing I and, indeed, Britney) - The Beat Goes On