Voyager flew by Triton in 1989, showing us an active world with an atmosphere, clouds, and erupting geysers. However, since then, we have only been able to study Triton from afar, and that situation will continue for the forseeable future. Only one data set, from the Hubble Space Telescope's Faint Object Camera in 1995, shows the resolved disk, barely. Below is the best I could get out of the HST views, which show one full rotation.
Bryan Flynn, the scientist behind this imagery, produced maps from the data, showing that the polar cap had enlarged since Voyager and hinting at variations between visible and ultraviolet images. Below are Flynn's maps:
Finally, here is a composite of Neptune and Triton I made from HST images from the mid 1990s. I hope that soon another telescope (or HST again) can image Triton at least at this resolution. Other data (light curves, spectra) have indicated increasing change, making continuing the baseline of coverage all the more important. With the discovery of planet size objects in the Kuiper belt, of which Triton is a captured member, understanding of this world is made all the more important. It is, after all, the only one we have seen closeup.