We present catalogs and images of optical counterparts to the Chandra X-ray sources found in the fields of the five rich clusters RX J0152-1357, RX J0849+4452, RDCS J0910+5422, MS 1054-0321, and RDCS J1252-2927, which were imaged with the Advanced Camera for Surveys as part of the ACS GTO programs. A total of 98 X-ray sources fall within the ACS mosaics and positive identifications are made for ~96% of them, including confirmed cluster members. We classify the sources as AGNs or QSOs depending on their X-ray output. The log N(>S)-log S test indicates a significant overdensity of X-ray sources in the RX J0152-1357, RDCS J0910+5422, and MS 1054-0321 fields with respect to the CDF-S, suggesting an association of some X-ray sources with the large scale structure of the clusters. From the asymmetry and concentration indices, ~52% of the optical counterparts are early-type galaxies, ~35% late-type, and the remainder irregular. A blue core is found in approximately half of the early-type galaxies. From visual examination, approximately 40% of the counterparts possess an unresolved nucleus, a common signature of nuclear activity. The X-ray to optical flux ratio of the nuclei correlates with the inclination angle of the late-type galaxies. The AGNs possess a ~50% excess of nearby companions compared to the overall galaxy population in the same fields. The surface density of the X-ray sources is highest at projected radii of <1 Mpc from the cluster center of RX J0152-1357, RDCS J0910+5422, and RDCS J1252-2927. We describe the morphology and environment of the cluster members. This research is supported by NASA grant NAG5-7697.
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