I think a common practice has been emerging during the last half-century, a new sense of harmonic clarity, often with a very slow rate of change. The mid-century avant-garde composers tended to use fast-moving harmonies that often encompassed the chromatic aggregate. For the listener, the result was often a dense and indefinable cloud; in any sense of the word, harmony was nullified, save for a purely theoretical structure. Composers such as Feldman, Riley, Scelsi, and Ligeti moved towards harmonies that were not only clearly defined but often slow-moving or static. These composers have had an enormous effect on musical thought in the U.S. as well as Europe. It was not entirely coincidental that minimalism and spectral music (where harmony is the foreground) arose at nearly the same time, as a reaction against modernism.
More recently, composers such as Mikel Rouse, Julia Wolfe, Luca Francesconi, and many others (including myself) have all made use of this kind of harmonic thinking. Although we all make use of different types of harmonies (sometimes purely tonal, others with microtones), harmony has become an important element in music, although not in the traditional tension/release formula of tonal-based music. Instead, harmony has become a purely coloristic device that lends a hue over the entire work. As in traditional music, each composer may present the harmony in many guises: repeated or sustained chords, contrapuntally, or even through electronic means (reverberation, resonance effects, etc.). Most importantly, harmonies are presented in an overt fashion, often over long stretches of musical time.