Globular Cluster Omega Centauri
Does an old, red globular cluster have any hot, blue stars? Photos taken in two wavelength bands, with comments on stellar evolution in the cluster.
http://www.phy.ncku.edu.tw/~astrolab/mirrors/apod/ap961004.html

Omega Centauri
Large color photo.
http://cfa-www.harvard.edu/~jpw/weird/omega_centauri.html

Omega Centauri: Nucleus of a Milky Way Dwarf Spheroidal?
A technical article from the Los Alamos E-print archive that discusses the possibility that Omega Centauri could be the remains (nucleus) of a once larger satellite dwarf galaxy that has been substantially reduced by tidal stripping caused by the Milky Way's disk.
http://arXiv.org/abs/astro-ph/9910278

Omega Centauri - a former nucleus of a dissolved dwarf galaxy?
A technical article from the Los Alamos E-print archive
http://arXiv.org/abs/astro-ph/0008500

NGC 5139 (Omega Centauri)
An image, links, data, and discussion from SEDS.
http://www.seds.org/messier/xtra/ngc/n5139.html