Since 1996 I have published on the Web a catalog of data for all known globular clusters in the Milky Way. The latest edition of the catalog is December 2010. The datafile is found here:
and the bibliography (source reference file and complete explanation of the various parameters and their calibrations) is here:
A link to another database of interest for globular cluster systems in other galaxies (by Duncan Forbes):
This how-to manual guides you through the use of all the standard subroutines in the IRAF implementation of Peter Stetson's DAOPHOT code for stellar photometry on CCD images.
Elizabeth Wehner has produced a catalog of magnitudes and colors in the Sloan Digital Sky Survey system (u'g'r'i'z') for the Landolt set of standard stars all around the sky. The UBVRI magnitudes from Landolt, A.U. 1992 (AJ 104, 340) have been transformed to the SDSS system with the equations given in Fukugita, M. et al. 1996 (AJ 111, 1748). The complete catalog is here.