The main visualisation tool of interest in image display is kvis. This tool allows you to inspect one or two 2- or 3-dimensional datasets in several ways. The simplest thing to use it for is displaying a dataset. kvis supports flexible zooming, special colour maps for velocity fields etc. For 3-dimensional datasets one can play the channels - as well as the RA-VEL and DEC-VEL slices - of the data cube as a movie, in order to get an idea of the 3D structure of the emission in the data cube.
kvis can load two datasets, which can then be viewed simultaneously in several ways, eg. blinking, or by displaying one data set as contour levels on top of the other. The advantage of kvis is that one has interactive control over zooming, contour levels etc., so it gives more flexibility than e.g. cgdisp. This mode of kvis can be used for overlaying a radio-continuum map on an optical image, or the channels of an HI data cube on the continuum or an optical image and inspecting this interactively. Note that for the contouring, the two datasets do not have to be on the same grid, although they should have a proper coordinate system defined. Also note that the visualisation software can read data in FITS format so one can load images from e.g. skyview directly and overlay Miriad datasets.
kvis can also produce full colour postscript output of whatever you display.